
Class _jGU * 5 3 

Book.. nTli. 

Copyright^ 

COPYRIGHT DEPOSIT. 



TWENTIETH CENTURY TEXT-BOOKS 



EDITED BY 



A. F. NIGHTINGALE, Ph.D., LL.D. 

SUPERINTENDENT OF SCHOOLS, COOK COUNTY, ILLINOIS 
FORMERLY SUPERINTENDENT OF HIGH SCHOOLS, CHICAGO 



TWENTIETH CENTURY TEXT-BOOKS 



ANIMAL STRUCTURES 



A LABORATORY GUIDE IN THE TEACHING OF 
ELEMENTARY ZOOLOGY 



BY 
DAVID STARR JORDAN 

PRESIDENT OF LELAND STANFORD, JR., UNIVERSITY 
AND 

GEORGE CLINTON PRICE 

ASSOCIATE PROFESSOR OF ZOOLOGY 




i j > j 



NEW YORK 

D. APPLETON AND COMPANY 

1903 






THE LIBRARY OF 
CONGRESS, 

Two Copies Received 

SEP 4 1903 

. Copyright Entry 

CLASS tXs XXc No 

COPY B, 



COPYRIGHT, 1903, BY 

D. APPLETON AND COMPANY 



Published, August, 1903 



PREFACE 



The present book is intended to cover the laboratory 
work in a course in zoology for beginners. In addition a 
more general idea of animals should be gained from lec- 
tures, from the study of some text-book of zoology, and, 
above all, from the observation and collection of animals 
in the fields and streams. 

Only a few forms have been chosen for study, experi- 
ence having shown that in a beginning course better results 
are obtained by spending the time in the thorough dissec- 
tion of a few forms than in the rapid study of many. 

Few illustrations are needed in this work. While it 
is true that the student will make more rapid progress 
with the picture of the dissection before him, it is equally 
true that what is thus gained in time is lost in power, the 
student being naturally tempted to rely upon the picture 
rather than upon his own work. 

The question as to the order in which the different 
forms should be taken up is largely one of convenience 
and individual preference. While in the present book we 
have followed the method of going from the simpler to the 
more complex forms, there is no reason why the order 
should not be varied, or even reversed at the desire of the 
teacher. 

David Starr Jordan, 
George Clinton Price. 
Leland Stanford, Jr., University, 
May S, 1903. 



ANIMAL STKUCTUEES 

ANIMAL CELLS 

Mount a drop of the blood of a toad or frog — that is, 
place a small drop of blood on a glass slide, and on it place 
a cover-glass. Examine under the microscope, using first 
the low and then the high power. 

Great numbers of small oval bodies, the red corpus- 
cles, will be seen. What is the color of these when viewed 
singly? When many are together ? 

Each corpuscle has the shape of a flattened oval disk. 
Perhaps you may see some turned on edge; they will then 
have the appearance of short rods. 

Scattered among the red corpuscles will be seen a few 
white corpuscles. They are not nearly so numerous as 
the red, are smaller, and are often of an irregular shape. 

Watch a white corpuscle carefully for a few minutes 
and see if you can detect any change of shape due to the 
pushing out of short processes from the edge and the 
drawing in of others. 

Both the red and white corpuscles are what are known 
as cells. The body of every animal and every plant is 
made up of cells, usually of great number of cells, of many 
different shapes and sizes, but some of the simplest ani- 
mals and plants consist of a single cell. 

The corpuscles consist of protoplasm, an extremely 
important substance, for it makes up the living part of 
every animal and every plant. The white corpuscles are 
almost pure protoplasm, but the red have in addition a 
coloring substance, called hcemogloiin. 

1 



2 ANIMAL STRUCTURES 

The protoplasm of a cell consists of two parts: the 
outer part, called the cytoplasm, and an inner -rounded 
body, the nucleus. Look for the nucleus in a red cor- 
puscle. It may be seen, but will not likely be very dis- 
tinct. Now place a drop of stain, methyl green or iodine, 
at the side of the cover-glass ; some of this will run in and 
come in contact with the corpuscles. The nuclei will now 
be seen distinctly, owing to the fact that they become 
stained much more readily than the cytoplasm. 

The vast majority of cells making up the body of an 
animal are not free as are the corpuscles, but are closely 
joined to one another, thus forming solid tissues. 

With a scalpel scrape the surfaces of your own tongue, 
mount the substance thus obtained, together with a small 
drop of water, and examine under the microscope. 

A few flattened cells will be seen, larger than the red 
corpuscles, and of a somewhat irregular, oval shape. Pos- 
sibly you may find several joined together. Stain, and 
see if you can find nuclei in any of them. 

In order to see that the solid tissues of an animal are 
composed of cells, place small pieces of the liver of a 
toad or frog, about the size of a grain of wheat, and also 
small pieces of the lining of the first part of the intes- 
tine, in a weak solution of chromic acid (1 part of acid 
to 5,000 parts of water), and allow them to remain in this 
for about twenty-four hours. 

Tease out a piece of liver in a drop of water on a 
slide — that is, tear it into as small pieces as possible — add 
a drop of stain, and cover with a cover-glass. Tap on the 
cover-glass, or press on it with the finger, at the same time 
moving it about. 

Under the high power of the microscope, look for more 
or less cube-shaped cells, each with a nucleus. Do you 
find any cases where a few cells are joined together? 

Examine a piece of the lining of the intestine that 



THE AMGEBA 3 

has been similarly treated, looking for elongated cells with 
one end perhaps a little larger than the other. 

THE AMCEBA 

Amoebae are very simple, microscopic animals found 
in the slime and mud at the bottom of fresh-water ditches 
or pools, or on the surface of submerged weeds and dead 
leaves. 

Some of this material, together with water, should 




c.v. 



Fig. 1. — A, the Amoeba, highly magnified, showing c. t>., contractile 
vacuole; /, food particle; w, nucleus. The arrows show the di- 
rection of movement. B, shape of same individual 30 seconds 
later. D, an Amoeba in the process of division (after Schulze). 

be brought into the laboratory and left standing for a 
day or two. 

With a medicine-dropper place a drop of the slime 
and water on a slide and cover with a cover-glass. Amoebae 
may be seen with the low power of the microscope, and 
after a certain amount of experience it will be best to 
search for them in this way, but at first it is better to use 
the high power, as they are much more easily detected with 
this than with the low power. First examine a strip 
around the edge of the cover-glass, not that the Amoebae 



4 ANIMAL STRUCTURES 

are more likely to be here than elsewhere, but in this way 
you will avoid going over and over the same area. * If not 
found here, then search on other parts of the slide. Look 
for an irregular, more or less granular, jelly-like mass. 
When found, watch closely to see if there is any movement. 
If so, it is in all probability an Amoeba. 

There are a number of different kinds of Amoebae 
which vary greatly in size, some being not much larger 
than a white blood-corpuscle, while others almost fill the 
entire field of the microscope, and could be seen as a 
minute speck with the naked eye. The large ones are the 
more desirable for study. 

Having found an Amoeba, observe the irregular proc- 
esses, the pseudopods, or false feet, projecting from vari- 
ous parts of the body. These are constantly changing, old 
ones being drawn in and new ones sent out. In some 
Amoebae the changes are quite rapid, in others so slow that 
they can be detected only by making a series of drawings 
at intervals of a minute or two. 

Amoebae have the power of locomotion — that is, of 
moving from place to place. This is done by sending out 
pseudopods from one side and drawing them in from the 
opposite side. 

The Amoeba is simply a mass of naked protoplasm, 
having no sort of a cell-wall nor cell-membrane surround- 
ing it. 

The protoplasm, or rather the cytoplasm, consists of 
two parts : a thin, clear, outer layer, the ectoplasm, and a 
granular, central mass, the endoplasm. Are you able to 
distinguish these? In some cases it is easy, in others 
difficult. When a pseudopod is formed, it is the ectoplasm 
which first pushes out, and into this the granular endo- 
plasm streams later. 

Observe the movement of the granules in the endo- 
plasm. 



THE AMCEBA 5 

Within the endoplasm you will likely see one or more 
relatively large bodies, simple plants, such as diatoms, 
which have been taken as food. To be sure of this, see 
if you can find similar bodies on the slide outside of the 
Amoeba. 

The Amoeba has no mouth, but takes in its food at 
any part of the body by sending out pseudopods and sur- 
rounding it. After remaining in the endoplasm some 
time, and after the soft parts have been digested, the innu- 
tritious part of the food is ejected from any part of the 
surface. See if you can observe either of these processes. 

Look for a small, clear, globular body, the contractile 
vacuole, which at regular intervals suddenly and entirely 
disappears, and then more slowly reappears. At first 
sight one might be inclined, on account of its pulsation, 
to compare this with the heart of a higher animal, but it 
is thought to have more the function of a kidney. 

Within the endoplasm is a rather large oval nucleus, 
which may sometimes be distinguished quite readily in the 
living animal, but usually only with difficulty, or not at 
all. If you have trouble in finding it, stain as you did in 
the case of the blood-corpuscles. Even then you may not 
be sure of finding it. 

From your study of the cells of the toad, you will 
readily understand that an Amoeba is a single cell. 

The process of reproduction is very simple; first the 
nucleus divides into two; then a constriction appears 
around the body, which becomes deeper and deeper, until 
the two parts thus formed are held together by only a 
slender strand. Soon this breaks, and instead of one 
amoeba there are two, each with its own nucleus. Look 
for cases of dividing Amoeba. They are not very com- 
mon. 

When the mud of the pond in which Amoebae lives 
dries, the animal assumes a globular form, secretes a hard 



6 ANIMAL STRUCTURES 

shell, or cyst, around itself, and remains dormant until the 
rains come. It then emerges from its cyst, and moves 
about as before. 

THE PARAMECIUM 

If a jar of water and water-weeds be brought in from 
a pond or stream it will in all probability contain a num- 
ber of different kinds of minute, one-celled animals, 
among them one called Paramcecium. But these animals 
are so small and relatively so few in number that you 
might look for a long time without finding a single one. 
If, however, the water be allowed to stand for a few days 
and to undergo putrefaction, the conditions will be favor- 
able for the rapid multiplication of the Paramcecia, so 
that every drop may contain a number of them. 

Place a drop of this water together with a 
little of the scum or debris from the culture jar on a 
slide, and cover with a cover-glass. Examine with the 
naked eye. The Paramcecia will appear as little white 
specks moving about in the water. ISTow place under the 
low power of the compound microscope. Do they appear 
to move more rapidly or more slowly than when viewed 
with the naked eye? At first it will seem impossible to 
study the creatures on account of their constant motion, 
but after a little time they will become more quiet. 

A Paramcecium is usually described as slipper-shaped, 
one end, corresponding to the toe, being more pointed, and 
the other, corresponding to the heel, more blunt. Which 
end is forward in locomotion? Does it ever move with the 
other end forward ? Observe that it sometimes turns over 
— that is, rotates on its long axis. Is it possible for the 
body to change shape ? To determine this point, watch the 
animals swinging around among the debris. 

Locomotion is caused by the vibration of cilia — deli- 



THE PARAMECIUM 



cate, hair-like projections of protoplasm — which cover the 

entire surface of the body. In order to see these, turn on 

the high power and bring the margin of the body into 

sharp focus. The cilia may be seen best at the pointed 

end, where they are less active; 

elsewhere they may be moving 

so rapidly that they can not be 

seen. It may be necessary to 

cut off some of the light, as the 

cilia can not be seen with too 

strong an illumination. 

Now bring either the upper 
or the lower surface into focus, 
and observe a great number of 
little dots arranged in rows. 
These mark the position of the 
cilia, but the cilia themselves 
can not be seen. 

The substance of a Para- 
mecium consists of proto- 
plasm, which is differentiated 
into an outer, firmer layer, the 
ectoplasm, and an inner, more 
fluid portion, the endoplasm, 
the whole being surrounded by 
a thin membrane, the cuticle, 
which comes into immediate 
contact with the ectoplasm and 
has numerous perforations, 

through which the cilia, which are projections of the ecto- 
plasm, protrude. 

Again bring the margin into focus. The ectoplasm 
and endoplasm may now be distinguished, the endoplasm 
by the moving particles in it, and the ectoplasm by the 
striated appearance which it presents, an appearance due 




Fig. 2. — ParamoBcium aure~ 
Ha, a ciliate infusorian. 
c, cilia; c. v., contractile 
vacuoles ; /, food vacu- 
oles ; g, esophagus ; m, 
buccal groove ; n, macro- 
nucleus. 



8 ANIMAL STRUCTURES 

to the presence of tricho cysts — structures to be studied 
later. 

Look for two clear globular bodies, the contractile 
vacuoles, which at regular intervals appear and then en- 
tirely disappear. How often does this occur? Are they 
constant in their position or do they move about? Are 
they situated in the center of the body, or near the sur- 
face ? To determine this point, observe an animal turn- 
ing over. 

An hour or so after the slide has been prepared enough 
of the water will have evaporated to allow the cover-glass 
to press lightly on the animals, and under these condi- 
tions the action of the vacuoles may best be studied. 
A number of clear rays will be seen around the vacuole, 
which, like the vacuole, appear and disappear. Make out 
the relation of these to the vacuole. The vacuole consists 
of a drop of water surrounded by highly contractile pro- 
toplasm, and when the latter contracts the drop of water 
is forced out of the body, but the fine canal, through which 
it passes, can not easily be seen. 

Among the particles moving about in the endoplasm 
will be a number of granular globules ; these are the food- 
vacuoles, each of which consists of a small drop of water 
containing a number of particles which have been taken 
into the body as food. 

On the side of the body usually turned down, observe 
a wide groove, the buccal groove, which, beginning at the 
blunt end, extends obliquely backward and to the right, 
ending in a funnel-shaped opening which leads into the 
endoplasm. The part corresponding to the stem of the 
funnel is known as the gullet or esophagus. The entire 
apparatus is ciliated, the cilia movivng in such a way as to 
sweep particles of food down into the endoplasm. 

In order to observe the process of feeding, rub up a 
little piece of carmine in water and place a drop at one 



THE PARAMECIUM 9 

side of the cover-glass ; if it does not run under it may be 
drawn under by placing a piece of blotting-paper on the 
other side of the cover-glass. Small particles of the car- 
mine will be swept into the gullet, at the inner end of 
which they will collect for a few seconds, and then, 
together with a small drop of water, will be suddenly 
swallowed, as it were, into the endoplasm. How often 
does this process take place? The food- vacuoles thus 
formed circulate in the same general direction through the 
endoplasm. Make out the course of this circulation. If 
food had been taken instead of carmine, it would ulti- 
mately have been converted into protoplasm; but the car- 
mine after a time will be expelled from the body at a point 
called the anal spot, situated below the end of the gullet. 
It is much easier to observe the act of swallowing than of 
the expulsion of the carmine. The water that is taken in, 
together with waste matter that becomes dissolved in it, 
is ultimately expelled through the contractile vacuole. 
Thus this organ serves as an excretory organ or kidney. 

Kun a little stain, such as methyl green, under the 
cover-glass. The animal will be killed, and a relatively 
large oval body, the macronucleus, which could not be 
distinguished before, will now be plainly visible. Lying 
right by the side of the macronucleus is a much smaller 
nucleus, the micronucleus, which also becomes stained, but 
is not easily distinguished. 

Around one of the dead individuals observe a great 
number of hairs, which might be mistaken for long cilia, 
but which are really trichocyst hairs, that have been sent 
out from the trichocysts in the ectoplasm. 

Occasionally an individual may be seen with a con- 
striction around the body about half-way between the two 
ends. It is then in the process of division, and should be 
watched under the low power. The constriction will be- 
come deeper and deeper, until finally the two parts will 



10 ANIMAL STRUCTURES 

be entirely separated, and two Paramcecia will exist 
where there was but one before. Under favorable condi- 
tions of food and temperature division may take place as 
often as every twelve hours. Starting with a single indi- 
vidual, how many would there be at this rate at the end of 
a week? 

Occasionally two individuals may be seen swimming 
about firmly attached together, with buccal groove toward 
buccal groove. They are then in the act of conjugation, 
and will remain thus attached for several hours. During 
this time important changes take place, which are not at 
all easy to follow, but which result in an exchange of 
nuclear matter. 

THE HYDEA 

Hydra are small, inconspicuous animals found at- 
tached to sticks, weeds, etc., in fresh-water ponds and 
pools, and in the sluggish parts of streams. They are of 
different kinds, some being of a green color, others 
brown, or almost colorless. 

If sticks and weeds to which hydra are attached be 
placed in a jar of water, after a time some of the Hydra 
will detach themselves, move to the side of the jar, and 
there become reattached. 

Examine such a jar which has been standing for at 
least a day or two. Do you find more Hydra on one side 
than on the other? If so, is it the side turned toward 
the light or away from it? Possibly you may find some 
specimens floating at the surface of the water. 

With a lens examine one of the animals while it is 
still attached to the side of the jar. It will be s.een to 
have an elongated cylindrical-shaped body, which is at- 
tached by one end, called the foot, while at the opposite, 
free end, a circle of long, slender arms, or tentacles, will 
be seen. 



THE HYDRA 



11 



Now remove a specimen from the jar to a watch-glass 
containing a little water. This may be done with a lifter, 
or still better with a long glass tube. Place a ringer over 
one end of the tube, and with the other loosen the speci- 
men. As soon as it is free, remove the finger. The Hydra 
will be drawn into the tube, and may be transferred to 
the watch-glass. 

Examine under the low power of the microscope. Pos- 
sibly the animal may soon reattach itself. This it does 




Fig. 3. — The fresh- water Hydra. A, entire animal, developing a 
new individual (enlarged 25 times) (after Schneider) ; D, section 
through the body; e.c, ectoderm; end, endoderm ; m, mouth. 



by means of a sticky substance secreted by the cells of the 
foot. Observe that the body has great power of changing 
its shape, at one time becoming long and slender, and at 
2 



12 ANIMAL STRUCTURES 

another short and thick. How ranch longer is it when 
fully extended than when fully contracted? When ex- 
tended, tap on the watch-glass and see if this has any 
effect on the animal. 

Have the tentacles the power of movement or of being 
lengthened and shortened? How many tentacles are 
there? Is the number the same for all individuals? 

The small; cone-shaped portion of the body beyond the 
base of the tentacles is the hypostome. 

At the end of the hypostome, and therefore in the 
center of the free end of the body, is the mouth. This 
can not well be made out except when food is taken, at 
which time it may open wide enough to take in an object 
larger than the diameter of the Hydra itself. 

Place a few small Crustacea, such as Cyclops or Daph- 
nia, in the watch-glass. In swimming about, one of them 
will come in contact with a tentacle, and will stop instantly, 
as if dead. After a time it will likely swim away, proving 
that it was not dead, but only paralyzed. The stinging 
apparatus by which this is done will be studied later. Is 
this Hydra able to paralyze another crustacean, or has it 
lost the power? 

If the Hydra is hungry, the crustacean will not escape, 
but will be drawn to the mouth by tentacles and slowly 
swallowed into the digestive cavity, called the enteron. 
Here it may be distinctly seen by the swelling caused in 
the body of the Hydra. It may require considerable 
patience to see the process of taking food, but one should 
not rest satisfied until he has seen it. 

After remaining in the enteron some time, perhaps 
several hours, and after all the soft parts have been 
digested, the shell of the crustacean will be thrown out at 
the mouth. 

These observations show that the hydra has a digestive 
cavity with a single opening to the outside. The tentacles 



THE HYDRA 13 

are all hollow, their cavities being continuous with the 
enteron. 

Place a specimen in a drop of water on a slide. To 
prevent its being injured by the pressure of the cover-glass, 
place some small object, as a bit of broken cover-glass or 
a small piece of water-weed from the jar, near it. Now 
cover. 

Examine with the high power of the microscope, taking 
great care not to break the cover-glass nor to crush the 
Hydra. When extended, bring the edge of the body into 
sharp focus, and observe the rather thin outer layer of the 
body wall, the ectoderm, and the thicker inner layer, the 
endoderm. In a green or brown hydra it is very easy to 
distinguish the layers, as the endoderm is colored, while 
the ectoderm is colorless. It is less easy to distinguish 
them in a colorless specimen, but even here it is not diffi- 
cult. While the microscope is focused in this way, you 
may possibly be able to distinguish the enteron extending 
through the center of the body. Occasionally particles 
may be seen moving up and down in it. 

Look for a clear, thin line separating the ectoderm 
from the endoderm. This is a supporting membrane, 
called the mesoglcea. 

Examine one of the tentacles. Are you able to distin- 
guish the ectoderm, endoderm, and mesogloea, and also 
the central cavity of the tentacle? 

The mesogloea is a non-cellular layer, but the ectoderm 
and endoderm are each made up of many cells attached 
side by side. It is not easy to distinguish the individual 
cells of the ectoderm in a living specimen, but it is quite 
easy to distinguish those of the endoderm. For this pur- 
pose, raise the objective until the specimen is out of focus, 
and then gradually focus down on the center of the body. 
First the ectoderm will come into view; then by focusing 
just a little farther you will see the outlines of the rather 



14 ANIMAL STRUCTURES 

large endoderm cells. Do these change shape as the body 
lengthens and shortens? Are yon able to make out the 
endoderm cells in the tentacles? 

When focusing on the ectoderm a number of clear, 
pear-shaped bodies will be seen, the nematocysts, or nettle 
cells, structures by means of which the Hydra paralyzes its 
prey. Extending into this nematocyst from the small end 
is a structure which will later be seen in a quite different 
position. If viewed from the end, instead of from the 
side, the nematocyst will appear round. Do you find 
nematocysts on the tentacles? Where are they most 
numerous? Are they in the ectoderm or endoderm?' 

Focus carefully along the edge of a tentacle and look 
for delicate, short hairs projecting out just a little from 
the ectoderm. These are the cnidocils, or trigger-hairs, 
structures which when irritated cause some of the cells 
of the ectoderm to contract and discharge the nemato- 
cysts. A cnidocil is not a part of a nematocyst. 

Bun under a drop of weak acetic acid, and in or near 
the tentacles look for rounded, flask-shaped bodies, with 
rather long, pointed necks, which are continued into a very 
long, slender hair. They are the discharged nematocysts. 
Do you find any barbs on the neck ? The neck and thread 
are hollow and are the structures seen on the inside of 
the undischarged nematocyst. The threads penetrate the 
body of an animal, and a poisonous fluid passes through 
it from the nematocyst. When discharged a nematocyst 
can not be used again, but new ones are all the time de- 
veloping. 

Lift up the cover-glass, remove the supports, and place 
a drop of methyl green upon the specimen. Xow replace 
the cover-glass and press on it until the specimen is 
crushed. Examine under the high power of the micro- 
scope. Some of the cells will be isolated. Among these 
look for some with nematocysts inside of them. These 



THE HYDRA 15 

are called cnidoblast cells, and are from the ectoderm. Do 
you find any of the endoderm cells? If it is a green or 
brown hydra they may be distinguished by the little round 
colored bodies they contain. 

Hydra reproduce both sexually and asexually. In the 
latter case a bud grows out from the side of the body, con- 
sisting of both ectoderm and endoderm, and contains a 
cavity continuous with the enteron. This grows larger 
and larger, a mouth and tentacles appear at the free 
end, the cavity of the new individual becomes sepa- 
rated from the enteron of the parent, and finally the new 
individual breaks away and leads an independent life. 

Look for a budding individual, and when found keep 
in a small vessel of water under observation from day to 
day until the new individual becomes free. 

Look for a specimen having two or three low, cone- 
shaped projections of the ectoderm on the body a little 
below the tentacles. These are the testes, or male repro- 
ductive organs. Examine a testis under the high power of 
the microscope. Possibly a great number of very small 
objects may be seen moving about inside. If so, they are 
the spermatozoa, or male reproductive cells. 

In the same or in another individual a larger rounded 
projection of the ectoderm, the ovary, may be seen. This 
is the female reproductive organ, and contains a large cell, 
the egg or ovum. 

It will be seen that one individual may have both male 
and female reproductive organs. Such an animal is said 
to be hermaphrodite. 

Individuals with buds are more numerous than those 
with testes, and those with testes than those with ovaries. 

If a hydra be cut into two or more pieces, each part 
will in time reproduce the lost parts and become a perfect 
individual. Try this experiment. 

If our own bodies were cut into halves from front to 



16 ANIMAL STRUCTURES 

back the resulting parts would-be exactly alike, and there 
is only this one plan through which they could be cut 
into similar halves. Such an animal is said to be bilater- 
ally symmetrical. A Hydra has neither right nor left side, 
front nor back, and it could be cut the long way through 
a number of planes so that the resulting halves would be 
exactly alike. Such an animal is said to be radially sym- 
metrical. 

THE STAKFISH 

As starfish live exclusively in salt water, the living 
animals can be studied only at the seashore. 

In a preserved specimen note the central dish, from 
which radiate five arms or rays. Observe that one side 
is flat, the other convex. The former is known as the 
oral side, the latter as the aboral side. The animal moves 
with the oral surface down. 

Note the numerous hard spines covering the body. 
Can you find more than one kind? 

Between the spines observe many soft, short bodies, 
the respiratory cceca. On what part of the body do they 
occur? They are blind tubes, like glove-fingers, and are 
connected with the body-cavity as glove-fingers are con- 
nected with the palm. During life the coelomic fluid may 
be seen, with a hand lens, circulating within them. 

Scrape off a little piece of the skin, tease it out on 
a slide, add a drop of solution of caustic potash, and under 
the low power look for the pedicillaria, little cone-shaped 
pincers at the end of short stalks. The jaws of the 
pincers have a calcareous skeleton which looks dark 
under the microscope. 

With a lens look for the pedicillaria on the surface of 
the body. If not visible, add a drop of caustic potash and 
look again. How widely are they distributed ? During life 
the jaws may be observed constantly snapping together. 



THE STARFISH 17 

In the center of the oral surface of the disk is a small 
opening, the mouth. Possibly some of the spines may be 
bent over so as to conceal it; if so, break them away with 
the forceps. Occasionally a part of the stomach may be 
seen protruding from the mouth. 

Immediately surrounding the mouth is a soft mem- 
brane, a part of the body-wall, the peristome. 

In the center of the aboral surface of the disk is a very 
small opening from the alimentary canal, the anus, which 
you will perhaps not be able to find. 

Along the oral side of each ray is a deep, wide groove, 
the ambulacral groove. 

Each groove is completely filled by the tube-feet, cylin- 
drical structures with sucking-disks at their end, which 
serve as organs of locomotion. With forceps pull out the 
tube-feet from a half inch of the groove a little distance 
from the end and examine them to see if they are tubes, 
as their name implies. Where the tube-feet have been 
removed, observe a number of holes, the ambulacral pores, 
through which the tube-feet communicated with certain 
internal structures. From these holes determine whether 
there is any regularity in the arrangement of the tube-feet. 

On the aboral surface of the disk, some distance from 
the center, and between two of the rays, is a round body 
an eighth of an inch or more in diameter, the madreporic 
body. Examine the surface with a lens. Can you find 
more than one madreporic body ? 

Because the madreporic body is situated between 
two of the rays, it is said to be interradial in position. 
Structures such as the tube-feet that are situated along 
or within the ray are said to have a radial position. 

Extending along the middle of the ambulacral groove 
is an inconspicuous ridge, the radial nerve. Here the 
nerve is a part of the skin, and not a distinct cord within 
the body, as is the case with most animals. 



18 ANIMAL STRUCTURES 

Follow the nerve toward its inner end. A short dis- 
tance from the mouth it will be seen to join the circum- 
oral nerve ring, a low ridge or fold which surrounds the 
mouth and connects the five radial nerves with one 
another. 

Now follow a radial nerve out to the tip of the ray. 
It will be found to end in a small red or orange-colored 
speck, the eye. 

In the body-wall is a sort of skeleton, made up of 
numerous small calcareous bodies called ossicles. Some 
of these, known as ambulacra! ossicles, may be seen in the 
ambulacral groove where the tube-feet have been removed. 
The ambulacral pores pass not through these, but between 
them. 

Cut off an inch or more of the end of a ray and 
place it for several hours in 20-per-cent nitric acid and 
observe the result. 

Cut off a quarter of an inch more of the same ray 
and boil it for a few minutes in a strong solution of 
caustic potash. The soft parts will be eaten away and the 
ossicles left free. Examine these. 

Look at the cut end of the ray and observe a large 
cavity, the body-cavity or ccelom. During life this cavity 
contains a nutritive fluid, called ccelomic fluid. 

The coelom is almost filled by two brown bodies, the 
pyloric cceca, portions of the digestive system. 

With stout scissors make a cut through the body-wall 
along both sides of the ray, and lift up the aboral portion. 
It will be seen that each pyloric caecum is suspended by a 
thin, double membrane, the mesentery. The body-cavity 
is lined by a thin membrane, the peritoneum. Can you 
separate this from the body-wall? 

Extending along the floor of the cavity of the ray, 
observe a prominent ridge, the ambulacral ridge. 

Eemove the dorsal body-wall from all the rays and the 



THE STARFISH 19 

disk, leaving the madreporic body, however, intact, and 
taking great care not to injure the internal organs. As 
some of these are attached to the dorsal body-wall, they 
should be carefully separated from the latter before it is 
lifted up. The digestive system will now be exposed. 

The pyloric caeca may have the appearance of solid 
bodies, but are really elongated sacks with much folded 
walls, the cells of which secrete a digestive fluid. Note 
that at their inner ends the two pyloric caeca of a ray unite 
and give off a single short duct. 

The cavity of the disk is occupied by the stomach, 
which is usually much lighter in color than the pyloric 
caeca. It is divided into a smaller upper part, the pyloric 
portion, and a larger lower part, the cardiac portion. The 
former is pentagonal in shape, and may be easily distin- 
guished by the fact that it receives the ducts of the pyloric 
caeca. 

A very short intestine leads from the center of the 
pyloric portion of the stomach to the anus, but this has 
likely been cut away, so that it can not now be seen. 

Lying upon the pyloric portion of the stomach, though 
not connected with it, is a branching body of doubtful 
function, the intestinal ccecum or respiratory tree. It is 
connected with the intestine. Is it arranged in five parts, 
as are most of the organs of the starfish? 

The cardiac portion of the stomach is immediately 
below the pyloric portion. It has thin and much folded 
walls, and gives off pouches, one for each ray, the cardiac 
cceca, which extend a little way into the rays. Lift up 
a cardiac caecum and note the two cardiac muscles 
attached along the side of the ambulacral ridge on the 
one hand and to the stomach on the other. 

Cut these muscles, lift the stomach still higher, and 
look for the very short esophagus leading from the mouth 
to the stomach. 



20 ANIMAL STRUCTURES 

Usually the starfish does not take its food into the 
stomach, but instead protrudes the cardiac portion of the 
stomach through the mouth, wraps it around the food, 
which usually consists of niollusks, and thus digests and 
absorbs the soft parts, leaving the shell perfectly empty. 
At the end of the process the stomach is drawn into the 
body by the contraction of the cardiac muscles. 

In each ray are two reproductive glands, testes in the 
male, ovaries in the female. They are attached to the sides 
of the body-wall near where the ray joins the disk. They 
vary greatly in size with the time of the year, being small 
at the close of the breeding-season, and gradually increas- 
ing as the next season approaches. They communicate 
with the exterior interradially through openings which 
are quite difficult to find. 

When ripe the eggs from the female and the sperm 
from the male are discharged into the water. Here they 
come in contact and the former are fertilized by the latter. 

Tease out a small piece of the reproductive organ in 
water on a slide and examine with the compound micro- 
scope. If ovary, large spherical cells will be seen — the 
eggs. If testis, a fine granular substance will be seen. 

Cut the stomach off near the mouth and remove it, 
together with the pyloric ca?ca. Along either side of the 
ambulacral ridge observe numerous small, bladder-like 
structures, the ampulla. They may be collapsed in the 
preserved specimen. Each ampulla is connected with a 
tube-foot by a fine tube, which passes through one of the 
ambulacral pores. 

At the cut end of the ray, look for a small round hole 
a little above the radial nerve. This is the radial water- 
tube, which extends the full length of the ray. It gives 
off fine tubes at right angles to itself, which join the tube- 
feet. Thus each tube-foot is connected both with an am- 
pulla and with the radial water-tube. 



THE STARFISH 21 

At their inner ends the radial water-tubes of the 
different rays are connected with a ring-vessel, which 
bears the same relation to the radial water-tubes that the 
circumoral nerve does to the radial nerves. This will be 
seen later. 

In some kinds of starfish there are thin-walled, pear- 
shaped vesicles, the polian vesicles, which extend into the 
rays a little distance and are attached interradially by a 
slender stem to the ring- vessel. 

Now look for an S-shaped tube, the stone-canal, lead- 
ing from the madreporic body to the ring-canal. Scratch 
it with the point of a needle to feel the calcareous par- 
ticles in its walls. 

With a hypodermic syringe or a medicine-dropper 
which has been drawn out to a fine point inject some col- 
ored fluid into the end of the radial vessel. If successful, 
the fluid will fill the tube-feet and ampullae of this ray, and 
passing through the ring-vessel, will also fill the radial 
vessels, ampullae, and tube-feet of the other rays, and may 
pass into the polian vesicles and stone-canal. 

During life the entire system, known as the water vas- 
cular system, is filled with a mixture of nutritive fluid 
and sea-water, the latter of which gains access through 
fine pores in the madreporic body. (However, it passes 
first into a little vesicle, and from this into the stone- 
canal.) 

You may possibly find a specimen in which one or more 
of the rays are shorter than the others. This is because 
the rays have been broken off and new ones are growing 
out, for the starfish has the power of reproducing lost 
parts. 

It will readily be seen that the starfish is for the most 
part a radially symmetrical animal. However, this radial 
symmetry is interfered with by the fact that there is but 
one madreporic body and one stone-canal, the plane pass- 



22 ANIMAL STRUCTURES 

ing through these structures being the only one along 
which the body could be divided into exactly similar 
halves. 

THE EARTHWOEM 

Place a living earthworm upon the table and observe 
its mode of locomotion by alternately lengthening and 
shortening the body. Compare this with the crawling of 
a fly. 

In locomotion one end is nearly always forward; this 
is known as the anterior end, while the opposite is the 
posterior end. One surface is always down and the other 
up; the former is known as the ventral, the latter as the 
dorsal surface. Can you notice any difference in shape 
between the anterior and posterior ends, or difference in 
color between the ventral and dorsal surfaces ? 

Place several worms in a jar of loose moist earth, and 
observe their mode of burrowing. Take them out and 
pack the earth as hard as possible. Are they able to bur- 
row in this? Cover the jar so the worms can not crawl 
out, and in a day or two observe the pellets of earth that 
have been cast out of the alimentary canal. In this way 
you may gain some idea of the amount of earth taken as 
food by worms. 

Now take a preserved specimen and observe that the 
entire body is divided into a large number of divisions, 
called segments, which are separated from one another by 
well-marked transverse grooves. The first division, called 
the prostomium, forms a sort of upper lip and is not a 
true segment. How many segments are there? Is the 
number the same for every worm ? 

About a third or a fourth of the distance from the 
anterior end there is a thickening of the skin forming 
a sort of girdle; called the clitellum. Counting from the 



THE EARTHWORM 23 

anterior end, what segments does this occupy? The 
clitellum is an accessory reproductive organ, it is not 
found on young worms, nor on the adults of certain kinds 
of worms except during the breeding seasons. 

Is the body of the earthworm divided into regions such 
as head, neck, trunk, and tail ? 

Draw a worm back and forth through the fingers and 
feel the bristles or setce. Look for these with the lens. 
Observe that they are arranged in rows. How many rows 
are there, and along what part of the body do they ex- 
tend? How many setae are there on each segment? By 
means of special muscles the setae may be pointed either 
forward or backward, and thus assist in locomotion by 
helping to anchor one part of the body while another is 
being moved. 

Note the two openings of the alimentary canal, the 
mouth at the anterior end just below the prostomium, and 
the anus at the extreme posterior end. Do you find any 
jaws or teeth connected with the mouth? 

On the ventral surface of the fifteenth segment look 
for a pair of openings, the apertures of the sperm-ducts. 
They are easily found, as each is guarded by a pair of 
prominent lips. On the ventral surface of the fourteenth 
segment look for the apertures of the oviducts. They are 
not conspicuous, and if difficulty is experienced in find- 
ing them, stretch the worm around the finger and look 
with a lens. 

Situated along the sides of the body and in the grooves 
between the ninth and tenth and tenth and eleventh seg- 
ments are two pairs of apertures of the spermathecce. 
They are quite difficult to make out. The four pairs of 
apertures just described will be found later to be con- 
nected with the reproductive system. 

There are two rows of excretory apertures extending 
almost the full length of the body about in line with the 



24 ANIMAL STRUCTURES 

apertures of the sperm-duets, but these are very difficult 
to make out. 

Stretch the worm around the finger and with a lens 
look for the dor sol. pores situated along the mid-dorsal 
line and in the grooves between the segments. How many 
do you find? 

There is a thin transparent covering, the cuticle, over 
the entire body. Perhaps you may be able to strip this off. 

Pin a specimen, dorsal side up. to the wax in the dis- 
secting pan by passing two pins through the sides of the 
body at either end. Cover with water. With a pair of 
fine-pointed scissors cut through the body-wall from the 
posterior to the anterior end along the mid-dorsal line, 
taking care not to injure any of the internal organs. 

At any point back of the twentieth segment gently 
pull the cut edges of the body-wall apart, the brown-col- 
ored intestine will be seen, and between this and the body- 
wall a series of spaces, separated from one another by deli- 
cate partitions called septa. Each septum is attached on 
the one hand to the alimentary canal and on the other to 
the body-wall. How do the septa correspond in number 
with the segments ? 

The spaces above mentioned are portions of an impor- 
tant cavity, the ~t><:>ji/-eavity or adorn, which extends the 
full length of the body, and within which all of the inter- 
nal organs are situated. It communicates directly with 
the exterior through the dorsal pores. 

The ecelom contains a clear nutritive fluid, the ccelomic 
fluid, which consists of a plasma in which float numerous 
corpuscles. It does not circulate in the true sense of the 
word, but may pass from one division of the ecelom to 
another through openings in the septa on the ventral side. 
Hold a living worm in the vapor of chloroform. The 
ccelomic fluid will exude through the dorsal pores and a 
drop may be collected on a slide and examined under the 



THE EARTHWORM 25 

microscope. Do you find amoeboid movement in any of 
the corpuscles? 

There is a well-developed circulatory system filled with 
red blood, the color of which is due to the presence of 
haemoglobin, but here the haemoglobin is dissolved in the 
plasma and is not located in the corpuscles as is the case 
with the blood of the vertebrates. 

Select a small, light-colored, living specimen, and ob- 
serve along the mid-dorsal line the pulsating dorsal vessel. 
Is the blood sent toward the anterior or toward the 
posterior end? 

Allow the worm to crawl along the inside of a bottle, 
and observe along the ventral side the non-pulsating 
ventral vessel. Examine with a lens. You will likely also 
see the much smaller subneural vessel. There are two 
other small longitudinal vessels on the ventral side, but 
these you will hardly be able to make out. 

Eeturn to the dissection. With a sharp scalpel 
cut all the septa along either side, noting their ab- 
sence in a few of the anterior segments, and pin out 
the flaps of the body-wall to the wax of the dissecting pan. 
The dorsal vessel will be seen imbedded in the walls of 
the intestine and presenting a beaded appearance. Fol- 
low it forward and in the sixth, seventh, eighth, ninth, 
and tenth segments find five pairs of branches, the so- 
called hearts, which pass around the alimentary canal and 
unite with the ventral vessel. Make out as much of this 
as you can without injuring any of the other organs. In 
addition to the hearts there is quite a complicated system 
of small vessels all along the body connecting the dorsal 
vessel with the longitudinal vessels on the ventral side, 
in some of which the blood passes dorsally and in others 
ventrally. 

The earthworm has no specialized respiratory organs, 
the entire surface of the body serving for that function. 



26 ANIMAL STRUCTURED 

The alimentary canal extends the full length of the 
body and consists £ various parts- 
Beginning anteriorly, note the white, thiek-walled 
pharynx from which numerous thread-like muscles pro- 
ceed obliquely backward and outward to be inserted into 
the body-wall. By the contraction of these muscles the 
pharynx is drawn backward and its cavity enlarged. This 
produces a suction which draws in any particles to which 
the mouth may be applied- 
Following the pharynx is the much smaller esophagus. 
It is partly concealed by the dorsal vessel and hearts, and 
by some large white bodies, the seminal vesicles, portions 
of the reproductive system. Gently press the seminal vesi- 
cles to either side, and carefully dissect away the blood- 
-els and the parts of the septa attached to the esopha- 
gus. This may now be seen as a slender tube somewhat 
enlarged posteriorly due to the presence of three pairs of 
pouches which open into the esophagus. 

Posterior to the esophagus thfe alimentary canal sud- 
denly enlarges to form the short crop. This is of a whitish 
color, but may appear dark, owing to the food contained 
within. 

Following the crop is the gizzard, which is about the 
same size as the crop. Make a longitudinal incision 
through the dorsal walls of the crop and gizzard, and note 
the relative thickness of their walls. In which segments 
are the different parts of the alimentary canal just de- 
scribed located? 

The intestine has already been mentioned. It will be 
seen to extend from the gizzard to the anus. Cut out 
about an inch of the intestine, open it along the ventral 
side, and wash out the contents. A longitudinal fold, the 
typlilosole, will be seen to project into the cavity from the 
dorsal side. 

The earthworm is hermaphrodite — that is, every indi- 



THE EARTHWORM 27 

vidual produces both eggs and sperm, but the eggs of one 
individual are always fertilized by the sperm of another. 
All this brings about a rather complicated reproductive 
system. 

The following is a list of the various organs: Female 
organs : One pair of ovaries, one pair of oviducts, one pair 
of egg-sacs, and two pairs of spermathecce. Male organs: 
Two pairs of testes, three pairs of seminal vesicles, and in 
some worms two median seminal vesicles, two pairs of 
seminal funnels, and one pair of sperm-ducts. All these 
are located in segments nine to fifteen. 

To serve as landmarks in determining the location of 
the various organs, pass pins through the flaps of the body- 
wall in the tenth and thirteenth segments. 

Place the specimen under a dissecting microscope or 
under a tripod lens. In the thirteenth segment gently pull 
the esophagus far enough to one side so that the white 
nerve-cord may be seen beneath, and observe the ovary, 
a small white body attached to the anterior septum near 
its union with the body-wall and a short distance from the 
nerve-cord. 

Facing the ovary on the posterior septum of this seg- 
ment is a whitish patch, the funnel of the oviduct. 

The oviduct is a very short tube, situated in the four- 
teenth segment, and extending downward, outward, and 
slightly backward from the funnel to open to the exterior 
about the middle of the segment. 

The egg-sac is a vesicle attached to the oviduct just 
at its beginning, and having somewhat the same relative 
position in the fourteenth segment that the ovary has in 
the thirteenth. After breaking away from the ovaries the 
eggs may be stored for a time in the egg-sacs. 

Press the seminal vesicles and esophagus slightly to 
one side in the ninth and tenth segments. In each a 
spermatheca will be seen as a rather conspicuous white 
3 



28 ANIMAL STRUCTURES 

body attaclied to the body-wall near the posterior boundary 
of the segment. The external opening has already been 
mentioned. The sperrnatheea? are vesicles in which the 
sperm from another worm is stored. 

Observe the three pairs of lateral seminal vesicles 
either partly or completely overlapping the esophagus. 
In which segments are they ? 

Remove the esophagus without injuring the seminal 
vesicles. Two median seminal vesicles will be exposed, one 
in the tenth segment, with which both the anterior and 
middle lateral seminal vesicles are connected, and one in 
the eleventh segment, with which the posterior lateral ves- 
icles are connected. (The median seminal vesicles are 
not present in young worms.) 

Remove the dorsal walls of the median seminal ves- 
icles. In each a pair of conspicuous white rosette-shaped 
bodies, the seminal funnels, will be seen. 

A little to the side of the point where the oviduct 
pierces the body-wall the sperm-duct may be seen. It is 
slightly imbedded in the body-wall, and is not always easy 
to see. Trace it backward to its external opening on the 
fifteenth segment, and forward to the twelfth segment, 
where it branches, then follow each branch to its union 
with a seminal funnel. 

In the same segments as the seminal funnels, and cor- 
responding in position with the ovaries, are two pairs of 
testes. These may be made out best in an immature 
worm. 

The testes produce cells which ultimately give rise to 
the sperm, but long before the sperm are formed they 
break away and become free in the seminal vesicles. Here 
they undergo repeated division, giving rise to a spherical 
structure consisting of a central portion surrounded by a 
layer of small cells, and presenting somewhat the appear- 
ance of a raspberry. Each of these little cells becomes 



THE EARTHWORM 29 

changed into a motile spermatozoon. Tease out a portion 
of a seminal vesicle in water and examine under the micro- 
scope. If the vesicle of a fresh worm be examined, the 
spermatozoa may be seen moving about. 

Remove a spermatheca, tease in water, and examine 
under the microscope. Sperm may possibly be found. 

Remove an ovary and examine under the microscope. 
At the free pointed end large spherical cells will be seen — 
the eggs or ova. 

With a lens observe along the body-wall on either side 
a series of white organs, the nephridia, each one of which 
extends from near the nerve-cord out toward the cut edge 
of the body-wall. These are the excretory organs or kid- 
neys, and occur in all the segments except the first three 
and the last. 

With the forceps pull away a nephridium, and 
under the microscope observe that it consists of a long 
tube bent back and forth several times and varying in 
diameter in different regions. One end opens to the exte- 
rior, the other pierces the septum and projects slightly into 
the segment in front, terminating in a funnel-shaped open- 
ing, the nepheostome. Look on the anterior face of a 
septum a little distance from the nerve-cord for the inner 
end of the nephridium. It is not always easy to find. 

Slightly chloroform a worm, cut into the body, and 
with the forceps pull out some of the nephridia, mount 
in water, and examine under the microscope. You will 
see what appears to be rapidly moving streams or cur- 
rents, but what is really the movement of the cilia within 
the lumen of the nephridium. 

Where the intestine has been removed a conspicuous 
white cord, the ventral nerve-cord, will be seen extending 
along the mid- ventral line. (It may be that the ventral 
blood-vessel will also be seen.) 

Remove the intestine and determine how far the 



30 ANIMAL STRUCTURES 

nerve-cord extends posteriorly. In the same way 
trace it anteriorly as far as the posterior end of the 
pharynx. Cut the muscles which extend from the 
pharynx to the body-wall, and follow the nerve-cord 
to where it divides into two cords, the circumpliaryngeal 
commissures. These bend up on either side of the pharynx 
and unite with the lower ends of the cerebral ganglia, two 
pear-shaped bodies lying on the dorsal side of the pharynx 
and united with one another in the mid-dorsal line. Thus 
it will be seen that there is a complete nerve-collar sur- 
rounding the pharynx. 

The cerebral ganglia, the circumpharyngeal commis- 
sures, and the ventral nerve-cord together form the 
central nervous system. 

Examine the cord with a lens. Slight swellings, 
known as ganglia, will be observed in each segment. 

Fine white threads may be seen given off from the cere- 
bral ganglia and from the nerve-cord. These are the 
nerves, which place the central nervous system in commu- 
nication with all parts of the body. How many pairs of 
nerves are given off in each segment? Possibly this may 
be determined better by removing a half-inch of the cord 
and examining it under the low power of the compound 
microscope. 

The body-wall is made up of three principal layers — 
an outer epidermal layer, a middle muscular layer, and an 
inner muscular layer. 

With forceps pull away a piece of the inner layer, ob- 
serving the fine threads, the muscle fibers, of which it is 
composed. In what direction do these fibers run? What 
effect would be produced by their contraction? 

Pull away all the inner layer from a few segments, 
and under the microscope examine the part of the body- 
wall that remains. Muscle fibers will be found which 
belong to the middle layer. In what direction do they 



THE EARTHWORM 31 

run? What effect would be produced by their contrac- 
tion ? 

Tear the preparation into small pieces and look for the 
rather small cylindrical cells of the epidermal layer. Some 
of these are glandular and secrete a mucus, which moist- 
ens the surface of the body ; others are sensory, being con- 
nected with the sense of touch. In this preparation you 
will likely see a number of pointed rod-like structures, 
the setae. 

In a preserved specimen cut the body in two through 
the region of the intestine, using either a sharp scalpel 
or a pair of sharp scissors; from one of the pieces cut off 
several sections not more than one segment thick. Wash 
out the contents of the alimentary canal, and with a lens 
look for the following parts: The intestine with its 
typhlosole, the septum, the blood-vessels, the nerve-cord, 
the nephridia, the setae, and the layers of the body-wall. 
Study a series of similar sections through the region of 
the reproductive organs. 

If a longitudinal section should be made through the 
middle of the body from the dorsal to the ventral side the 
resulting halves would be alike, and this is the only 
plane in which it could be cut into similar halves. Such 
an animal is said to be bilaterally symmetrical. 

The eggs of the earthworm are laid in capsules which 
somewhat resemble a grain of wheat, except that there is 
no crease on the side. These may be found with little 
trouble by looking through a shovelful of earth in a place 
where worms abound. Cut into a capsule and observe that 
it is filled with albumen, like white of egg. It may also 
contain young worms large enough to be seen with the 
naked eye. If no worms are seen, mount the albumen on 
a slide, and under the microscope look for eggs or small 
worms. 



32 ANIMAL STRUCTURES 

THE CRAYFISH 

In either a living or preserved specimen note the body, 
to which are attached, along the ventral side, a number of 
pairs of appendages. 

The body is obviously divided into two parts — a pos- 
terior abdomen, consisting of a number of rings or seg- 
ments, movably articulated with one another, and an ante- 
rior cephalothorax, which at first sight shows no signs of 
segmentation. 

The cephalothorax is further divided into an anterior 
head and posterior thorax, a transverse groove, the cervical 
groove extending obliquely downward and forward from 
the dorsal side marking the boundary between the two. 

The back and sides of the cephalothorax have a con- 
tinuous covering, called the carapace. 

Anteriorly the carapace is produced into a pointed 
structure, the rostrum, which varies in shape in the differ- 
ent kinds of crayfish. The part of the carapace posterior 
to the cervical groove is divided into a small central car- 
diac area, beneath which the heart is situated, and two 
large lateral flaps, the branchiostegites, which form the 
lateral boundaries of the branchial or gill chambers. The 
branchiostegites are marked off from the cardiac area by 
slight lines or grooves, the branchio cardiac grooves, which 
extend from the cervical groove to the posterior edge of 
the carapace. 

See if you can pass a dissecting needle into the gill 
chamber between the ventral edge of the branchiostegite 
and the base of the legs. 

How many segments are there in the abdomen? In 
what particulars do the first and last segments differ from 
the others? The last or posterior segment is called the 
telson. On its ventral side is the anus, the posterior open- 
ing of the alimentary canal. 



THE CRAYFISH 33 

Observe that the abdomen may be bent well forward 
under the cephalothorax. How far can it be bent in the 
opposite direction? Can it be bent from side to side? 
Try to make out the mechanical arrangement which per- 
mits motion in certain directions and prevents it in others. 

The crayfish is completely enclosed in a case or cover- 
ing called an exoskeleton, which is very firm and hard, 
except at the joints, both of the body and appendages, 
where it is thin and flexible. What is the advantage of 
this? The exoskeleton is not composed of cells, and is 
therefore not a living tissue, but is a cuticular structure 
secreted by the cells of the thin skin beneath. It is com- 
posed of a substance called cliitin, which is rendered firm 
and hard by the deposition in it of lime in every place 
except at the joints. 

Place a specimen in a jar of 20-per-cent nitric acid. 
This will remove the lime, but will not act upon the chitin. 
What change is produced? One specimen will do for an 
entire class. 

In another specimen carefully separate the abdomen 
from the cephalothorax, and boil for half an hour or so 
in a strong solution of caustic potash. The soft parts 
will be eaten away, leaving only the exoskeleton and the 
lining of the esophagus and stomach. There should be 
at least one such specimen for every four or five students. 

Make a further study of the way in which the rings of 
the abdomen are joined together, for this purpose separat- 
ing them from one another. The dorsal part of one of these 
rings is called the tergum (plural terga), the parts ex- 
tending freely down on the sides the pleura (singular 
pleuron), and the part between the appendages the 
sternum (plural sterna). 

Though the carapace is continuous with the rest of the 
exoskeleton, it may with a little care be broken away with- 
out injuring either it or the part below. This should now 



34 ANIMAL STRUCTURES 

be done. In the head, observe the stomach, or rather the 
lining of the stomach, which is attached by the esophagus 
to the mouth below. The lining of these organs is of the 
same nature as the exoskeleton and at the mouth is con- 
tinuous with it. 

Again examine the cephalothorax for indications of 
segmentation, paying especial attention to the ventral side, 
both inside and out, and to the side walls, which have been 
exposed by the removal of the cephalothorax. 

At intervals of a year or more in old individuals, but 
more frequently in young, the exoskeleton becomes free 
from the skin, a break occurs on the dorsal side between 
cephalothorax and abdomen, and through this the animal 
backs out, leaving the exoskeleton in so perfect a condi- 
tion that at first sight it has the appearance of a real cray- 
fish. This process is called ecdysis or molting. Before 
the old exoskeleton is thrown off a new one is started. 
At first this is very soft, and while in this condition the 
animal increases so in size that it seems impossible it could 
have come out of the old exoskeleton. In a few days the 
new exoskeleton becomes hardened by the deposition of 
lime, and no further increase in size can take place until 
the next molt. 

If possible, examine a living animal, observing which 
appendages are used in walking, the way in which objects 
are seized by the pincers, the movement of the many 
jointed feelers and of the eyes, and the force with which 
the abdomen may be bent downward and forward. This 
is a swimming motion, and causes the animal to dart 
backward swiftly when in the water. 

Observe bubbles coming off from two points on the 
ventral side of the head; they are given out from the cer- 
vical canals, which lie just below the ends of the cervical 
groove and lead from the gill chambers. Hold the animal 
firmly by the back, and from the anterior end look into the 



THE CRAYFISH 35 

cervical canal; a long thin plate, the scaphognathite, will 
be seen moving up and down in it. This moves in such a 
way as to bail the water or air out of the gill chamber. 

Now hold the animal under water, ventral side up, and 
with a pipette drop some water containing powdered car- 
mine along the base of the legs; soon this will be seen 
streaming out from the cervical canal. It will thus be 
seen how fresh water is passing constantly through the 
gill chamber for the purpose of respiration. Can a cray- 
fish live out of water ? 

Break away the entire branchiostegiti from one side 
of a preserved specimen, and expose the gills. Each gill 
consists of a central stem, to which numerous filaments 
are attached. Move some of the appendages back and 
forth and observe that certain of the gills are caused to 
move. This is because they are attached to the basal joints 
of the appendages. Gills so attached are called podo- 
branchia. ISTow move each of the appendages in the region 
of the gills in succession, and determine the ones to which 
gills are attached, and how many are attached to each 
appendage. 

Carefully turn down the podobranchia. (This may 
best be done under water.) A new set of gills will be 
exposed. These are attached to the membrane con- 
necting the basal joint of the appendages with the body. 
best.be done under water..) A new set of gills will be 
hence called arthrobranchia. How do they compare in 
number with the podobranchia ? What is the total number 
of gills? 

If a specimen of the genus astacus from the Pacific 
slope be examined, look for a gill attached to the body- 
wall above the last thoracic appendage. This is known as 
a pleurobranchia. In a corresponding position in front of 
this, look for rudimentary gills, each one of which resem- 
bles a single filament of one of the functional gills, 



36 ANIMAL STRUCTURES 

Beexarnine the caustic potash preparation. Were the 
gills eaten away by the caustic potash? What does this 
show ? 

With sharp scissors cut off one of the gills near its 
base, and with a lens examine the cut end of the stem. 
Two blood-vessels will be seen, one of which conveys the 
impure blood to the gill, the other conveys the pure blood 
away from it. From the first small side branches are 
given off to the filaments, and these connect with other 
fine branches which empty into the second. While passing 
through the gills, the blood is separated from the water 
by only a thin membrane, and through this the earbon- 
dioxid of the blood passes to the water and the oxygen of 
the water passes to the blood. 

Now turn back the gills. A number of vessels, the 
branchiocardiac canals, will be seen in the body-wall pass- 
ing from the base of the gills and converging toward the 
dorsal side. They convey the pure blood from the gills 
to the pericardial sinus. 

The crayfish has nineteen pairs of appendages. These 
differ greatly in size and structure on different parts of 
the body, and going along with this difference of structure 
will be found a remarkable difference of use of function. 
An important fact which may readily be observed is that 
the appendages are jointed. 

If an appendage is lost, as is often the case, a new 
one grows out. but it is some time before it becomes 
as large as its fellow of the opposite side. Look for ex- 
amples of this. 

Begin the study of the appendages with those of the 
fifth abdominal segment. Xote the basal part, the pro- 
topodite. to which are attached two branches or rami, the 
inner one being called the endopodite, the outer the ex~ 

lite. Such an appendage is known as a biramous ap- 
pendage. How many joints are there in the protopodite? 



THE CRAYFISH 37 

Are there any in the endopodite or exopodite? Note the 
numerous hairs or setce on the endopodite and exopodite. 
In the female, the egg and later the young are attached 
to these. 

Compare the last pair of appendages with the ones 
just studied. Are they biramous? Are they attached to 
the telson, or to the sixth abdominal segment? Observe 
that they can be spread out, so that together with the tel- 
son they resemble a fan. This fan, or tail fin, is a very 
efficient swimming organ when the abdomen is flapped 
forward. 

Eemove the appendages just examined from the same 
side as that on which the gills have been studied, and con- 
tinue to do this with the others, as fast as they are studied 
placing them in order on a card. 

In the female all the abdominal appendages with the 
exception of the last are like those of the fifth segment; 
but those of the first somite may be very small or entirely 
wanting. 

In the male the appendages of the first and second 
segments are modified to serve as accessory reproductive 
organs, being used to transfer the sperm to the female. 
Observe that they are bent forward under the cephalo- 
thorax. 

Next come five pairs of large appendages, the ambula- 
tory appendages, the four posterior of which are used for 
walking, while the anterior, which are much larger than 
the others, serves by means of their powerful pincers or 
chelce as a weapon of offense and defense, and are also 
used in seizing food and conveying it to the mouth. 

Examine one of the posterior ambulatory appendages. 
Is it biramous? How many joints has it? Note that 
while all the joints are hinge-joints, like our elbow, a wide 
range of movement is obtained by their being in different 
planes. If a male, look for the opening of the sperm-duct 
on the first or basal joint. 



38 ANIMAL STRUCTURES 

Examine in succession the next four appendages, com- 
paring them with the one just studied and carefully noting 
resemblances and differences. In the female, look for the 
opening of the oviduct on the basal joint of the third 
appendage. In removing the appendages be careful that 
the podobranchia, but not the arthrobranchia, are also 
removed. 

Next come six pairs of appendages, which are crowded 
close together and serve as mouth parts, being used in the 
process of mastication. Of these, the posterior three are 
known as maxillipedes, and belong to the thorax. How 
many pairs of thoracic appendages are there? 

Examine the third or last maxillipede. Observe that it 
is biramous. The protopodite is made up of two joints, 
the second of which is fused with the first of the endop- 
odite. Can you find teeth any place on this appendage 
that might assist in mastication? 

At first one is inclined to look upon the ambulatory 
appendages which have the pincers or chela? as biramous. 
Compare one of these with the third maxillipede, and see 
if such an interpretation is correct. Imagine the exopo- 
dite removed, and compare the part that is left with one 
of the walking appendages. The latter might be looked 
upon as a biramous appendage that has lost the exopodia, 
the first and second joints representing the protopo- 
dite, and the remainder the endopodite. This is be- 
lieved to be the case, and in the lobster, which closely 
resembles the crayfish, it is actually the case; for when 
the young lobster hatches the ambulatory appendages have 
both exopodite and endopodite, and later the exopodite 
is lost. 

The second maxillipede resembles in general the third, 
but is smaller, and the relative size of the exopodite and 
endopodite is reversed. 

In the first maxillipede, observe that instead of a 



THE CRAYFISH 39 

podobranchia there is a thin leaf -like structure extending 
into the gill chamber. 

The other three pairs of appendages, which act as 
mouth parts, belong to the head, and are, beginning with 
the posterior, the second maxillce, first maxillce, and man- 
dibles. 

The second maxilla is much modified, and it is hard to 
recognize the parts of a biramous appendage in it. Note 
especially the scaphognathiti, which is a part of this ap- 
pendage, and which has already been seen in the living 
animal. 

The first maxilla is considerably smaller than the 
second. 

Between the first maxillae and the mandibles are a pair 
of small, leaf-like plates, which are outgrowths of the 
border of the mouth, and are not looked upon as an ap- 
pendage. 

The mandible is a hard, bony structure, with a three- 
jointed palp fitting into a groove on its anterior surface. 
Observe the teeth along its inner edge. The mandibles 
form the chief organs of mastication. They are worked 
by powerful muscles, which will be seen later. 

Between the mandibles observe the mouth, and note 
that it is situated some distance back of the anterior end 
of the body. 

In front of the mandibles there is a considerable space 
free of appendages, and then come two pairs which func- 
tion as sense organs, the first and second antennce. These, 
of course, belong to the head. What is the total number 
of head appendages? 

In the second antenna, note the hard, sharp-pointed 
plate which forms the exopodite, and the endopodite, 
which consists for the most part of a long, many-jointed 
feeler. On the ventral side of the basal joint observe a 
slight protuberance, upon which is a small pore, the ex- 
cretory aperture. 



40 ANIMAL STRUCTURES 

The first antenna is smaller than the second. Both 
exopodite and endopodite are many-jointed feelers. 

Make a table of the appendages, giving their function 
and the part of the body to which they belong. 

Remove the carapace from the cardiac area and from 
the head region as far forward as the base of the rostrum, 
and about half-way down on the sides. In order to do this 
without injuring the internal organs, insert the point of 
the scalpel under the posterior edge, and, keeping it in 
contact with the hard part, work it forward, and break 
away the carapace bit by bit. In like manner remove the 
exoskeleton from the dorsal side of the abdomen. 

If the work has been carefully done, the delicate shin 
will now be exposed. Remove this. 

Beneath the cardiac area the heart may now be seen, 
a light-colored, thick-walled, muscular sac. From the an- 
terior end are given off a median ophthalmic artery, a 
pair of antennary arteries, and below these a pair of 
hepatic arteries, while from the posterior end, near the 
ventral side, are given off, very close together, two median 
arteries, the sternal artery, which passes straight down- 
ward to the ventral side, and the dorsal abdominal artery, 
which passes backward above the intestine. All these are 
difficult to see on account of their delicacy and transpar- 
ency, but will be studied later in an injected specimen. 

On the dorsal surface of the heart look for a pair of 
openings, the ostia. Now remove the heart and look for 
two more pairs of ostia, one on the sides and one on the 
ventral surface, and at the same time look for the openings 
where the arteries have been broken away. Make a cut 
through the heart and note the cavity and the thickness 
of the walls. 

The cavity in which the heart is situated is the peri- 
cardial sinus. This is an essential part of the circulatory 
system, for the branchiocardiac canals, which convey the 



THE CRAYFISH 41 

blood from the gills, empty directly into it and not into 
the heart. 

When the heart expands the blood passes from the 
pericardial sinus through the ostia into the heart; when 
it contracts it passes out through the arteries, being pre- 
vented from passing back into the pericardial sinus by the 
valves which guard the ostia. 

In a living specimen insert a scalpel under the cara- 
pace into the pericardial sinus and collect the colorless 
blood which issues from the wound. Examine a drop 
under the microscope. Do you find any corpuscles? 
Allow the remainder to stand for a while. Does it coag- 
ulate ? 

On either side of the pericardial sinus observe a long, 
light-colored muscle. Find its attachment at either end; 
determine what effect would be produced by its contraction. 

Beneath the pericardial sinus will be seen the repro- 
ductive organs. These consist in the male of a light-col- 
ored, three-lobed testis, one lobe being directed backward 
and two forward, and a pair of greatly convoluted sperm- 
ducts. Tear away the thin ventral wall of the pericardial 
sinus and press the sperm-ducts to either side, so that the 
various lobes of the testis may be distinguished. Carefully 
straighten out one of the sperm-ducts, tracing the one 
end to its connection with the testis and the other to its 
external opening on the basal joint of the last thoracic 
appendage. 

In the female the ovary has the same relative position 
as the testis in the male, and like the testis is a three-lobed 
organ. It varies greatly in size with the time of the year, 
but is always much larger than the testis. Press the body- 
wall to one side and observe the short, straight oviduct 
passing off from the side of the ovary. Follow it down to 
its opening on the basal joint of the third ambulatory 
appendage. 



42 ANIMAL STRUCTURES 

Xote the stomach which had already been seen in the 
caustic-potash preparation. With the finger-nail move 
one of the mandibles from side to side, at the same time 
observing that a body at the side of the stomach is caused 
to move up and down. This is the muscle which causes 
the mandible to close. 

Observe the anterior gastric muscles, which are at- 
tached on the one hand to the anterior dorsal surface of 
the stomach and on the other to the carapace near the 
base of the rostrum, and the posterior gastric muscles, 
which are attached to the posterior dorsal surface of the 
stomach and to the carapace near the cervical groove. The 
simultaneous contraction of these muscles tend to pull the 
anterior and posterior ends of the stomach apart. Later 
we shall see what effect this produces. 

Press the dorsal muscles of the abdomen away from 
the middle line, and observe the straight intestine which 
passes from the stomach to the anus. This, with the 
exception of a very small part next to the stomach, has 
a chitinous lining like the esophagus and stomach. 

Remove the reproductive organs; they will be found 
to lie upon a pair of yellowish or brownish bodies, the 
posterior ends of the digestive glands, usually called the 
liver. How far forward do these extend? Each gland 
is made up of a great number of caeca, like glove-fingers, 
which unite together and empty by a common duct into 
the side of the intestine near where it joins the stomach. 
They secrete a digestive fluid, and, in addition, some of 
the food may pass from the intestine into the glands and 
from here be absorbed in the blood. 

Press the posterior ends of the digestive glands to 
the side and observe the intestine passing between them. 
Try to see where the duct joins the intestine. 

Remove the digestive glands, cut the anterior gastric 
muscles, and pull back the stomach. The esophagus may 



THE CRAYFISH 43 

now be seen. Cut this near its connection with the stom- 
ach and remove the latter. As has been said, the lining 
of the stomach is of chitin. This has been thickened and 
strengthened at certain places by the deposition of lime, 
so as to form what are known as gastric ossicles, which 
form a sort of framework to the stomach. These may be 
quite readily distinguished, but may be seen to better ad- 
vantage in the caustic-potash preparation. 

Make a slit from the esophagus up through the ante- 
rior wall of the stomach, and wash out the contents. Look 
into the large anterior chamber of the stomach, and in the 
posterior part observe the single median and the two 
lateral gastric teeth, which may readily be distinguished 
by their brown color. They are connected with the frame- 
work of gastric ossicles, which are hinged together in 
such a way that when the gastric muscles contract the 
teeth are brought together. Pull the anterior and poste- 
rior ends of the stomach apart and observe the movement 
of the teeth. 

The part of the stomach in front of the gastric teeth 
is known as the cardiac portion, and the part back of them 
as the pyloric portion. 

There is a single pair of excretory organs, often called 
kidneys or green glands, situated in the head below the 
bases of the second antennae. Each organ is a disk-shaped 
body, to which is attached a bladder, which lies upon it 
and which opens to the exterior through the excretory 
aperture on the basal joint of the second antennae. With 
a glass tube drawn out to a point, inflate the bladder with 
air through the aperture, being careful to push the tube 
in only a very short way. 

Eemove the dorsal muscles of the abdomen, and ob- 
serve the very heavy ventral muscles, noting their continu- 
ation forward on the floor of the thorax. Make out the 
anterior attachment of the latter to the exoskeleton of the 
4 



44: ANIMAL STRUCTURES 

thorax. What would be the effect of the contraction of 
these muscles? Remove the ventral abdominal muscles, 
noting the way in which the different strands are looped 
over one another. 

The abdominal portion of the ventral nerve-cord will 
now be seen extending along the mid-ventral line. Along 
this cord observe a number of slight swellings, the ganglia, 
from which pass off fine, white cords, the nerves. How do 
the ganglia compare in number with the segments? Is 
there a ganglion in the telson? In the posterior part of 
the thorax the cord will be seen to enter a sort of tunnel. 
Examine this tunnel in the caustic-potash preparation, 
and observing its anterior opening. 

Break away the roof of the tunnel and expose the 
cord. How do the ganglia compare in number with the 
appendages ? The cord is pierced by the sternal artery. 
Look for this, or if the artery has been removed, for the 
opening through which it passed. 

With stout scissors cut away the body-wall on one side 
to a level with the base of the appendages, and follow the 
large nerves from the ganglia into the appendages. In the 
region corresponding to the mouth-parts a number of 
nerves will be seen given off close together. This has been 
brought about by the crowding together and fusion of 
several ganglia into one. 

Just anterior to this the cord divides into two com- 
missures which pass forward on either side of the esopha- 
gus and reunite in the cerebral ganglion in the very ante- 
rior part of the head. 

Break away the exoskeleton down to the level of the 
cerebral ganglion and look for the nerves passing to the 
eyes and to the first and the second antennae. Are there 
any other nerves given off from this ganglion? 

Eemove one of the first pair of antennae, and under 
the low power of the microscope look for little bunches of 



THE CRAYFISH 45 

hairs on the exopodite, the olfactory setce. These are 
thought to be connected with the sense of smell. 

On the dorsal side of the basal joint of the same 
appendage look for an opening guarded by a thick bunch 
of setae. This leads into a sac which forms the ear or 
organ of hearing. Break away the wall from the ventral 
side of this joint and expose the sac. 

Kemove one of the eyes, and with a lens — or, better, 
with the low power of the microscope — examine the dark 
surface. It will be seen to be divided into a great number 
of square areas called facets. With a scalpel divide the 
eye longitudinally and observe the dark mass within. This 
is made up of a great number of complicated, rod-like 
elements, called ommatidia, each ommatidium correspond- 
ing to a facet. KScrape out some of this mass, tease it 
out a little in a drop of water, and examine under the 
microscope. Possibly the whole or parts of some of the 
ommatidia may be seen. An eye like this is called a com- 
pound eye. 

The arteries may be quite easily injected by passing 
the needle of an ordinary hypodermic syringe forward 
under the posterior edge of the carapace into the peri- 
cardial sinus. The specimen should be left some hours for 
the injection mass to set. Open the specimen as in the 
previous dissection, and trace out the arteries which have 
already been mentioned (p. 40), the ophthalmic, the 
antennary, the hepatic, and the dorsal abdominal. Fol- 
low the sternal artery ventrally, observing that it pierces 
the ventral nerve-chain and then divides into two branches, 
one running backward, the ventral abdominal artery, and 
another running forward, the ventral thoracic artery. 
From the ventral thoracic artery are given off branches 
which may be traced out into the appendages.. 



46 ANIMAL STRUCTURES 

THE GRASSHOPPER 

Grasshoppers are familiar insects found in great abun- 
dance in the fields during the summer and fall. There 
are a number of different kinds, but any kind will do for 
study, the larger specimens, of course, being preferable 
for dissection. 

The body of the grasshopper is divided into three 
regions : head, thorax, and abdomen. Of these the head 
is easily distinguished; the thorax is the part which bears 
the legs and wings, while the abdomen is the long, dis- 
tinctly segmented posterior region. These parts will be 
studied more in detail later. 

With forceps seize the wing by the lower edge, and 
pull it outward and forward. A second wing will be dis- 
closed, which is attached to the body back of the first. 
Pull this out in like manner. Let it go and observe that it 
folds up like a fan. Does the first wing fold also ? Which 
wing is the larger ? Which is the stiffer ? The first wings 
are sometimes called the wing covers. Cut off one of the 
second pair of wings close to the body, spread it out on 
a slide, and examine with a lens. Observe the thickened 
ridges, the veins, diverging outward from the base. They 
give strength to the wing. The main veins are connected 
by numerous small transverse veins, and in this way the 
wing is divided into a great number of clear areas called 
cells. Do you find veins and cells on the first wings also? 

On the front of the head observe the single pair of 
many- jointed antennce, special organs of feeling which 
contain in addition the olfactory organs or organs of 
smell. 

At the lower end of the head are a number of struc- 
tures, known collectively as mouth-parts. These are the 
labrum, one pair of mandibles, one pair of maxillce, the 
labium, and the hypopharynx. 



THE GRASSHOPPER 47 

First find the unpaired flap-like upper lip or labium, 
which is movably articulated to the lower part of the front 
of the head. 

Cut this away and expose the strong, dark-colored jaws 
or mandibles. These are powerful organs of mastication. 
Insert a scalpel between them and open them, noting their 
toothed inner edges, and also the direction in which they 
move. Compare this with the direction in which your own 
jaws move. 

Break away the mandibles. They are followed by a 
second pair of jaws, the maxillae. In which direction do 
they move? A maxilla is not so simple a structure as a 
mandible, but is made up of a number of parts. Of these 
note the sharp, dark-colored biting part, and the jointed 
palp. 

Break away one of the maxillae, being careful to get 
all of it and examine more carefully. 

Following the maxillae is the median lower lip or 
labium. Though unpaired, it is formed by the fusion of 
a pair of structures resembling the maxillae. Do you find 
any indication of this fusion? The labium is made up of 
a number of parts. Of these note the jointed palps. 

Just in front of the labium is a median tongue-like 
structure, the liypopliarynx. 

Of the mouth-parts the mandibles, maxillae, and labium 
are modified appendages, while the labrum and hypo- 
pharynx are not. The antennae are also appendages, so 
that there are in all four pairs of appendages on the head. 

There are three pairs of appendages on the thorax, the 
legs. The wings are not reckoned as appendages, being 
of an entirely different structure. 

Each leg is made up of a single series of joints. Ex- 
amine one of the first pair. The first joint — that 
which joins the body — is the coxa. This is followed by a 
still smaller joint, the trochanter. Next comes a stout 



48 ANIMAL STRUCTURES 

joint, the femur. Next another long joint, but more 
slender, the tibia. The part beyond the tibia is the tarsus, 
and consists of more than one joint. Of how many ? On 
the tarsus observe a pair of sharp hooks and a series of 
pads. Would these pads rest on the ground in the natural 
position ? 

Now return to a study of the body. First cut off the 
wings, leaving short stumps. The head joins the thorax 
by a short neck. Is any movement possible between head 
and thorax? One might think the head represented a 
single somite, corresponding to one of the somites of the 
abdomen, but it is thought to have been formed by the 
complete fusion of several segments. 

The thorax consists of three divisions, each correspond- 
ing to a segment: The prothorax, which bears the first 
pair of legs; the mesothorax, which bears the second pair 
of legs and the first pair of wings; and the metathorax, 
which bears the last pair of legs and the last pair of 
wings. With this in mind, are you able to find the boun- 
daries between the different divisions? Is there any 
movement between prothorax and mesothorax ? Between 
mesothorax and metathorax? The prothorax is covered 
on the sides and back by a structure, called the pronotum, 
the free edge of which extends back a little over the 
mesothorax. 

Examine any one of the segments in the middle region 
of the abdomen. It will be seen that the exoskeleton — 
that is, the outer covering — is made up of a larger dorsal 
piece, the tergum, and a smaller ventral piece, the sternum, 
the two being joined together on either side by an infold- 
ing of the wall. These infoldings of the various segments 
give rise to a conspicuous groove extending along either 
side of the abdomen. 

How many abdominal segments are you able to dis- 
tinguish ? You will have trouble in determining just what 



THE GRASSHOPPER 49 

are segments at the posterior end. This is really a difficult 
point, and has led to a difference of opinion as to the num- 
ber of segments in the abdomen. 

The tergum of the anterior segment is easily distin- 
guished, but the sternum is dovetailed into the sternum 
of the metathorax, so that it looks more like a part of the 
thorax than of the abdomen. Then the tergum and ster- 
num of this segment do not come together on the sides, 
the bases of the last pair of legs intervening, so that at 
first sight one might think the legs belonged to the first 
abdominal segment rather than to the metathorax. 

Thus the boundary between thorax and abdomen is not 
very clear, especially on the ventral side. Examine some 
other insect, such as a fly, ant, bee, or wasp, and see if the 
division into the three body regions — head, thorax, and 
abdomen — is any more clearly marked than in the grass- 
hopper. At the same time see if the number of legs is 
the same. 

On the sides of the upper part of the head observe the 
pair of large compound eyes. In addition look for three 
small simple eyes, one in the middle line between the 
antennae and one just in front of the upper part of 
each compound eye. With a scalpel slice off one of the 
compound eyes, place it on a slide, and scrape out the 
dark soft part within. First examine the hard outer part 
under the microscope. It will be found to be transparent 
and to be divided into a great number of hexagonal areas 
called facets. Corresponding with each facet is a com- 
plicated rod-like element of the compound eye called an 
ommatidium. Tease out the soft part of the eye in a 
drop of water and examine under the microscope. Possi- 
bly you may be able to see some of these, or at least parts 
of them. 

On the side of the first abdominal somite look for a 
rather large oval opening across which is stretched a thin 



50 ANIMAL STRUCTURES 

membrane, the tympanic membrane. This is thought to 
be an organ of hearing. 

Just in front of the tympanic membrane find with a 
lens a small opening, a stigma or ~breathi?ig-pore. Find 
another above and a little back of the base of the second 
leg, and still others on the abdomen just above the groove 
running along the side of the body. How many do you 
find on the abdomen? Do you ever find more than one 
pair on a segment? In breathing, air passes through the 
stigmata into tubes called tracheae, which will be studied 
later. No air is taken in through the mouth. 

Every part of the grasshopper — body, wings, and ap- 
pendages — is enclosed in a tough, more or less flexible exo- 
skeleton, formed of a substance called chitin. The exo- 
skeleton is not the skin, nor is it formed of cells, but is 
secreted by the cells of the true skin beneath. While the 
animal is growing it casts off the exoskeleton at intervals, 
and develops a new and larger one. This casting of the 
exoskeleton is called the ecdysis. 

Examine a living specimen, observing the movement of 
the antennae and mouth-parts, the breathing movements 
of the abdomen, the way in which the animal walks and 
leaps, and the way it holds to an object with its feet. 

Examine a number of specimens, either living or pre- 
served, and observe that in some the end of the abdomen 
is more pointed, in others more blunt and rounded. The 
former are females, the latter males. At the end of the 
abdomen in the female observe two pairs of pointed proc- 
esses, the ovipositors. 

If possible use a fresh specimen for studying the inter- 
nal anatomy; but if not, a preserved specimen will do. 

Cut away the labium, spread the mandibles wide apart, 
and with a lens look for the mouth between the base of 
the mandibles and in front of the base of the hypo- 
pharynx. 



THE GRASSHOPPER 51 

Cut away the exoskeleton from the front of the head, 
and between the eyes observe the large light or yellowish 
cerebral ganglion or brain. 

Below the brain find the dark-colored esophagus ex- 
tending upward from the mouth and passing beneath the 
brain. In order to see this it may be necessary to pick 
away some of the soft parts. 

Cut away the exoskeleton from the dorsal side of the 
thorax and abdomen, bend out the body-wall a little on 
either side, and with pins fasten down to the wax of the 
dissecting pan. Cover with clear water. In the anterior 
part of the thorax a part of the dark-colored alimentary 
canal may be seen, but part of the canal will be covered 
by the reproductive organs — so it will be necessary to first 
study these. 

In a female the ovaries are conspicuous yellow bodies, 
occupying a large part of the dorsal region of the abdo- 
men and even extending into the thorax. The size varies, 
however. Each ovary is made up of a series of ovarian 
tubules lying side by side and extending obliquely back- 
ward, outward, and downward from the middle line. 

Separate the ovaries along the middle line and turn 
the tubules of each outward. All the tubules of a side will 
be found to be attached to a rather large, light-colored 
oviduct, which extends backward under the alimentary 
canal, where it joins its fellow of the opposite side. The 
single tube thus formed leads to the exterior. A part of 
each oviduct will be seen to extend forward beyond the 
point where it is joined by the first tubules. 

The free end of each ovarian tubule will be seen to 
become suddenly very slender and light in color. Re- 
move a tubule and examine under the low power of the 
compound microscope. It will be found filled with eggs, 
the one nearest the base being large, elongated, and yel- 
low, while the others are much smaller and decreased in 



52 ANIMAL STRUCTURES 

sue :: T "ard the end. The very end of the tube is a slender 
filament which contains no eggs. 

In the male the two testes are closely bound together, 
forming a conspicuous body lying above the alimentary 
canal in the middle region of the abdomen. From either 
side is given off a sperm-duct, or vas deferens, which, like 
the oviduct, passes beneath the alimentary canal and 
unites with its fellow of the opposite side. Tease out 
the testes, and with a lens observe the numerous tubules 
of which they are composed. In both male and female 
there are accessory parts of the reproductive organs, but 
these will not be studied. 

If you have been studying a fresh specimen, you have 
doubtless already noticed some of the bright, silver-col- 
ored trachea, or breathing tubes. Examine with a lens 
and note their branching. In a preserved specimen the 
tracheae are far less conspicuous and may perhaps not 
be detected with the naked eye. In either case mount a 
little of the soft tissue and examine under the compound 
microscope. You can scarcely fail to have some of the 
tracheae, as they go to every part of the body. They lo k 
something like a closely wound spiral spring, an appear- 
ance due to the spiral thickening of their chitinous lining. 
The tracheae communicate with the exterior through the 
stigmata, and here their chitinous lining is continuous 
with the chitinous covering of the body. 

If it has not already been done, remove the ovaries 
or testes, and expose the alimentary canal along its entire 
length. 

In the region of the thorax some rather large light- 
colored bodies, the gastric ceeca, will be seen lying on the 
alimentary canal. Each is made up of a larger anterior 
and a smaller posterior caecum, which are free at their 
ends but unite with each other at their bases and open 
together into the alimentary canal. 



THE GRASSHOPPER 53 

Farther back observe a tangled mass of long, slender, 
brown tubules arising in a circle from the alimentary 
canal. These are the Malpighian tubules, and serve as 
excretory organs or kidneys. 

Cut the alimentary canal in the anterior part of the 
thorax, turn it back, at the same time breaking or cutting 
the tracheae which bind it to other parts. Free it along 
its entire length and place it in a small vessel of water. 

The alimentary canal is divided into a number of 
regions. First is the esophagus, which was seen leading 
upward from the mouth and passing beneath the brain. 
Just back of the brain it enlarges into the crop or inglu- 
vies. This is the part that was cut. The crop passes 
without any marked change of size into the ventriculus, 
but the boundary between the two may be determined by 
the fact that it is into the very beginning of the ventricu- 
lus the gastric caeca empty. Following the ventriculus 
comes the intestine. Here, again, there is no well-marked 
boundary to be seen from the outside, but it is just in 
front of the openings of the Malpighian tubules, they 
arising from the intestine. Three regions are recognized 
in the intestine : the ileum, the first straight portion ; the 
colon, the portion w r here the intestine makes a sudden 
bend; and the rectum, the enlarged terminal region. 

With scissors slit open the alimentary canal along 
its entire length, remove the contents, and under water 
float it out on a slide with the inside up. Examine with 
the naked eye or with a lens. Are you able to deter- 
mine the boundary between crop and ventriculus, and 
between ventriculus and intestine? The esophagus and 
crop and the intestine have a delicate chitinous lining, 
while the ventriculus has not. 

One part of the central nervous system — the brain — 
has already been seen. Now look for three rather large 
ganglia on the floor of the thorax, and, extending from 



54 ANIMAL STRUCTURES 

one ganglion to another, a pair of slender nerves, called 
commissures. Do yon find any nerves passing out from 
the ganglia ? Find commissures extending backward from 
the last thoracic ganglion and follow them until you 
come to a swelling, the first abdominal ganglion. Pro- 
ceed in like manner to the end of the abdomen. How 
many abdominal ganglia do you find? Do they give off 
any nerves? Follow the commissures forward from the 
first thoracic ganglion. In the head, just back of the 
esophagus, they unite with a subesophageal ganglion, and 
connecting this with the brain are two circumesophageal 
commissures passing on either side of the esophagus. 

The grasshopper has a circulatory system, the princi- 
pal part of which is a long pulsating heart situated along 
the dorsal side of the abdomen. Its walls are thin, and 
the blood which it contains is colorless, so that it is quite 
hard to make out. 

THE FBESH-WATER MUSSEL 

The fresh-water mussel is a bilaterally symmetrical 
animal, much compressed from side to side, and enclosed 
within a shell composed of two parts or valves, hence 
called a bivalve shell. The shell is never shed, but con- 
tinues to increase in size as long as the animal lives. It 
does not grow itself, but is secreted by the soft parts 
beneath. On the outer surface are a number of concentric 
lines, called lines of growth, which mark the size and 
shape of the shell at various stages of its growth. These 
are seen to converge toward a slight protuberance known 
as the umbo, situated at the dorsal side of the shell and 
near the anterior end. The umbo is the oldest part of 
the shell. 

Place a living specimen in a vessel of water containing 
3 or 4: inches of fine sand. In a little while the shells will 



THE FRESH-WATER MUSSEL 55 

open slightly at the two ends and along the ventral 
side, and from the anterior ventral side a white, tongue- 
shaped body, the foot, which is the organ of locomotion, 
will be protruded. This will be sent down into the sand, 
and immediately the animal will begin to turn with its 
dorsal side up, at the same time moving forward and 
burying itself. With an active individual this may require 
only a few minutes. 

The burying will not be complete, the posterior end 
remaining above the surface of the sand. At this end 
observe two rather large openings leading into cavities 
within the shell. The lips of the more ventral opening 
are beset with numerous short tentacles. W r ith a pipette 
place a few drops of water containing powdered carmine 
near these openings. It will be found that a current of 
water is steadily passing in through the more ventral 
opening, hence called the inhalant aperture, while a cur- 
rent is at the same time passing out through the more 
dorsal opening, the exlialant aperture. The water thus 
taken in serves for the purpose of respiration, and at the 
same time carries microscopical animals and plants which 
form the food of the animal. Touch the lips of the 
exhalant or inhalant aperture. The shell will be imme- 
diately closed. 

Before proceeding with the dissection it will be best 
to study the inner surface of an empty shell. Note the 
smooth iridescent surface. Some shells have ridges and 
projections near the dorsal edge on either valve, which 
fit into corresponding depressions of the opposite valve, 
thus forming a sort of hinge. These belong to the genus 
Unio. In others, belonging to the genus Anodonta, the 
ridges and projections are entirely wanting. 

Concentric with the ventral edge and a little distance 
from it is a well-marked line, the pallial line. This ends 
anteriorly at an oval area, the anterior adductor impres- 



56 ANIMAL STRUCTURES 

sion, and posteriorly at a somewhat similar area, the pos- 
terior adductor impression. During life the muscles 
which close the shell, the anterior adductor and the pos- 
terior aductor, are attached at these points. Near-by 
are other smaller impressions to which muscles that assist 
in protruding and retracting the foot are attached. 

In a preserved specimen in which the shell is gaping 
observe the thin lamella, the mantle lobe or pallial lobe, 
lining each valve. Insert the point of a scalpel between 
this and the shell, and determine whether it is simply 
in contact with the shell or whether it is attached to it, 
and if so, where. If any attachment is found loosen it, 
and then, keeping the point of the scalpel in contact with 
the shell, sever the anterior and posterior adductor muscles, 
and the other muscles near them, from their attachment 
with the shell. As soon as this is done the valves will open 
more widely than before. Press them together and notice 
that some resistance is offered, and that when released 
they at once spring apart. This is due to the elasticity of 
the hinge-ligament, an uncalcified part of the shell join- 
ing the two valves along the dorsal line. 

Break off the loosened valve and place a piece of the 
broken hinge-ligament and a fragment of the shell in acid 
to determine whether they contain lime, the presence of 
which will be indicated by effervescence or bubbling. 

The body proper is now visible, lying in one-half of 
the shell. Note the position of the adductor muscles, and 
observe that they extend from one valve to the other. 

Make out the attachment of the mantle lobe to the 
body. Is it of equal thickness throughout ? Does it line 
the entire shell? 

Observe that the inhalant opening leads into a large 
chamber, the branchial cavity, which is bounded laterally 
by the mantle lobes, and that the exhalant opening is con- 
nected with a much smaller cavity, the supr -abranchial 



THE FRESH-WATER MUSSEL 57 

cavity, which extends forward below the posterior ad- 
ductor. During life the edges of the mantle lobes are 
in contact every place except at the inhalant and exhalant 
openings, so that the branchial cavity is virtually com- 
pletely closed except for the inhalant opening. 

The posterior end of the alimentary canal is on the 
dorsal side of the posterior adductor, and opens through 
the anus into the posterior part of the suprabranchial 
chamber. This part of the chamber is sometimes spoken 
of as the cloaca. Just back of the anterior adductor is 
the mouth. 

Turn back the mantle lobe. A number of important 
organs will be seen suspended in the branchial cavity. In 
the anterior half is a large median body, the ventral part 
of which is the foot, previously seen projected from be- 
tween the valves in the living specimen; the larger, 
thicker, dorsal part is the visceral mass, within which 
will be found later several important organs. The ante- 
rior part of the foot projects somewhat beyond the vis- 
ceral mass. 

Extending from the posterior end of the branchial 
cavity to beyond the middle of the visceral mass will be 
seen on either side two leaf-like bodies, the gills. On the 
floor of the suprabranchial cavity observe four rows of 
openings, and make out the relation of these to the gills 
by passing a pin into some of them. Each gill is really 
a sort of pouch or pocket, divided into a great number of 
compartments by cross-partitions. These cross-partitions 
may easily be seen from the suprabranchial cavity. Can 
you see any markings on the surface of the gills corre- 
sponding to the internal divisions? 

The walls, or lamella, of the gills are pierced by many 
fine pores through which the water passes from the 
branchial chamber into the compartments of the gills. 
From these it passes up into the suprabranchial cavity, and 
thence out through the exhalant opening. 



58 ANIMAL STRUCTURES 

Anteriorly the suprabranchial chamber divides into 
four parts, one for each gill. Make this out by passing 
a seeker forward in the cavity above the base of each gill. 
In the angle between the inner gill and the visceral mass 
there is a direct communication between the branchial 
and suprabranchial chambers, and through this the seeker 
will pass into the branchial chamber. Make out the extent 
of this opening. 

In front of the gills on either side are two triangular 
bodies, the labial palps, which might be taken for small 
gills, but which are entirely different structures. The 
outer palp of one side is joined to the outer palp of the 
other side by a narrow fold extending around in front of 
the mouth, while the inner palps are similarly connected 
by a fold passing back of the mouth. The surfaces of 
the palps are covered with cilia, which move in such a 
way as to sweep food particles toward the mouth. 

The pericardial cavity is a median chamber situated 
in front of the posterior adductor muscle and dorsal to the 
attachment of the mantle lobe with the body. The lateral 
walls are very thin, so that its size and location may be 
easily determined. 

Make an opening into the cavity. It contains the 
heart, consisting of two auricles and one ventricle, and in 
addition is traversed by a portion of the intestine. The 
ventricle surrounds, and looks like an enlargement of the 
intestine. 

An artery is given off from either end of the ventricle, 
the one passing forward above the intestine, and the other 
passing backward below it. They can not be seen at this 
stage. 

But one auricle can now be seen. It has a narrow 
attachment to the side of the ventricle on the one hand 
and a much broader attachment to the lateral part of 
the floor of the pericardial cavity on the other. Its walls 



THE FRESH-WATER MUSSEL 59 

are very thin, and are usually collapsed, so that it presents 
the appearance of a thin triangular membrane. 

The blood, which is colorless, is received into the auri- 
cles, these contract and send it into the ventricle, the 
ventricle then contracts and sends it through the two 
arteries above mentioned and their branches to all parts 
of the body. That which goes to the mantle lobes is 
returned directly to the auricles, while that which goes 
to other parts of the body has to pass through both the 
gills and the kidneys before it again reaches the auricles. 

Take out the portion of intestine within tha pericardial 
cavity together with the ventricle. In order to do this 
the auricles will have to be severed. Xow with scissors 
make a transverse section, passing through the openings 
between auricles and ventricle. Look into the cut ends 
and make out the relation between ventricle and intes- 
tine. Is there any communication between the two ? See 
if you can find valves which would allow blood to pass 
from the auricles to the ventricle, but would prevent its 
flowing in the opposite direction. 

Make a section through the intestine in front of the 
heart, and look at the cut end for the artery given off 
from the ventricle. 

It will be well at this stage to open a living speci- 
men and observe the beating of the heart. (A single speci- 
men will likely answer for an entire class.) With scissors 
cut off small pieces of the gills and labial palps and 
examine them under a compound microscope for the 
action of the cilia. With a scalpel scrape off cells from 
the surface of the visceral mass, foot, and mantle, and 
determine whether these parts are also ciliated. It is the 
action of the cilia which causes the currents of water to 
pass into the branchial cavity and out of the supra- 
branchial cavity. 

Eeturning to the preserved specimen, note the dark 
5 



BO ANIMAL STRUCTURES 

color of the floor of the pericardial cavity, due to the 
presence of the excretory organs, which are situated imme- 
diately beneath the floor of this cavity. 

Look for two small openings, a right and a left, on 
the anterior part of the floor of the pericardial chamber 
near where the intestine enters. These are the reno- 
pericardial openings, leading from the pericardial cavity 
into the excretory organs. 

Cut away the mantle lobe close to its union with 
the body, turn back the gills, and look for two small 
openings, very close together, in the angle between the 
inner gill and the visceral mass, and just below the reno- 
pericardial opening. The anterior of these is the renal 
aperture leading from the excretory organ, and the poste- 
rior the aperture of the reproductive organ. There are two 
similar openings on the other side. 

The excretory organs consist of a single pair of wide, 
thin-walled tubes. Each tube begins at the renoperiear- 
dial opening and extends back as far as the posterior ad- 
ductor muscle. This part has dark irregular walls and is 
often called the Yxdney. At its posterior end the tube 
turns and runs forward above the kidney and below the 
floor of the pericardial cavity, ending at the external open- 
ing mentioned above. This part is sometimes called the 
ureter. Through part of its course it communicates with 
the ureter of the other side. Make an opening into the 
bend of the excretory organ just in front of the posterior 
adductor muscle, and pass one seeker forward in the ureter 
and another in the kidney. Then open the two parts, 
noticing the relation of one to the other, and also the dif- 
ference in their wa' 

Cut through the floor of the suprabranchial chamber, 
and on the ventral surface of the posterior adductor mus- 
cle just beneath the skin observe the visceral nerve 
ganglia, two ganglia united into one body. 



THE FRESH-WATER MUSSEL 61 

Pull away the skin from the side of the body opposite 
the corner of the mouth and look for the cerebral gan- 
glion, a small spindle-shaped usually orange-colored 
body from which several branches are given off. One 
of these branches, the cerebral commissure, will be seen 
to pass forward and around to the cerebral ganglia 
of the opposite side. Does it pass above the mouth or 
below it? 

Follow another branch, the cerebro-visceral connective, 
which proceeds at first upward and backward, and then 
arches around to unite with the visceral ganglion. This 
will require care and patience. 

Trace another branch, the cerebro-pedal connective, 
downward and backward to its connection with the pedal 
ganglion, situated at the boundary between the foot and 
visceral mass. This is quite difficult, as the connective 
passes through tough muscle almost the color of itself. 
There are two pedal ganglia, a right and a left, closely 
joined together. 

Pare away the wall from the side of the visceral mass 
and expose a granular substance which appears to fill the 
entire visceral mass. This forms the reproductive organs 
— testes in the male, ovaries in the female. In either case 
the structure is the same, there being a great number of 
little sacs, called follicles, in which the sex cells develop, 
and which communicate with the exterior on either side 
through ducts opening at the reproductive aperture. 
Tease out some of the reproductive organ in water and 
examine with a compound microscope. If a female, the 
ova may be distinguished as large spherical cells, but in 
a preserved male the spermatozoa can hardily be dis- 
tinguished. 

When ripe, the eggs pass into the cavity of the outer 
gill, where they remain for a long time and undergo the 
first part of their development. Perhaps some individuals 



62 ANIMAL STRUCTURES 

with thick outer gills have been met with. If so, examine 
the contents under the microscope. Eggs or young in 
some stage of development will be found. When the 
young leave the gills they attach themselves to the body of 
a fish, where they remain for some time and undergo a 
metamorphosis. They then drop into the mud as young 
mussels. Those that do not become attached to a fish 
perish. 

Continue to pare away the side of the visceral mass 
toward the anterior end. In this region a greenish body 
will be found, the digestive gland. This was partly ex- 
posed in tracing back the cerebro-visceral connective. 
The gland secrets a digestive fluid, which is poured into 
the stomach through several ducts. 

Pass a seeker into the mouth and up through the 
short esophagus, which lies just back of the anterior 
adductor muscle. Open up the esophagus from the side 
and trace it to its opening into an enlarged cavity, the 
stomach. Open the stomach, and on the side wall find 
the openings of the digestive gland, and on the floor 
the opening into the intestine. 

Under water scrape away the reproductive organ and 
expose the intestine. Its walls are so tender and it is so 
closely invested by the reproductive organs that there is 
danger of scraping away the intestine itself. Do you 
find the intestine straight or convoluted? Trace it to its 
connection with the stomach on the one hand, and into 
the pericardial cavity on the other. The part passing 
through the pericardial cavity as well as the extreme pos- 
terior end which passes over the posterior adductor mus- 
cle have already been seen. 

Remove a well-hardened specimen from the shell, place 
it upon a board, and with a scalpel — or, better, with a 
razor — cut it into a series of transverse sections about a 
quarter of an inch thick. Place these in order in the dis- 



THE FRESH-WATER MUSSEL 63 

secting pan under water. A number of points of the 
anatomy will be better understood from the study of the 
sections than from the dissection. 

Find the anterior and posterior adductor muscles. 
Observe the relation of the mantle lobes and of the gills 
to the body. 

Study the relation of the suprabranchial chamber to 
the gills, and find sections where it shows as a single 
chamber, where it is divided into three parts, and where 
it is divided into four, one for each gill. 

Note the relation of the foot to the visceral mass, and 
observe that the latter is almost completely filled by the 
reproductive glands. 

Embedded in the reproductive glands find sections of 
the various coils of the intestine. Look for sections of 
the intestine in which the lumen is crescent-shaped. This 
is due to the fact that for some distance in front of the 
heart the wall of the intestine folds down into the lumen, 
forming what is known as a typlilosole. 

In the more anterior sections find the stomach and 
the digestive glands, and observe the position of the latter 
relative to the reproductive glands. Examine with a lens 
looking for the very numerous cceca of which the diges- 
tive glands are composed. 

In a section passing through the heart region observe 
the relation of the heart to the pericardial cavity, of the 
auricles to the ventricle, and of the ventricle to the 
intestine. 

Just below the floor of the pericardial cavity observe 
two smooth-walled tubes, the ureters. Possibly the sec- 
tion may be taken through the place where the ureters 
connect with each other, in which case there would be a 
single wide tube. Below the ureters observe two tubes 
with folded walls, the kidneys. 

In the middle line between the ureters a small tube 



64 ANIMAL STRUCTURES 

may be seen, one of the blood-vessels. Other blood-ves- 
sels may be seen at the base of the gill lamellae. 

You may possibly be able to distinguish parts of the 
nervous system also. 

THE TOAD 

Kill a toad by placing it in a tight jar with a piece 
of cotton saturated with chloroform. This specimen may 
be studied in the fresh conditon for a day or two, depend- 
ing on the temperature, but after that it should be placed 
in 70-per-cent alcohol or 2-per-cent formalin to pre- 
serve it. 

A white secretion will be poured out from glands of 
the skin. Wash this off. Do you find any scales on the 
skin? 

The body is made up of head and trunk, there being 
neither neck nor tail. 

Compare the hind leg with the leg of man and the 
fore leg with the arm. Do you find parts corresponding 
to thigh, leg, and foot ? and to arm, forearm, and hand ? 
and joints corresponding to knee and ankle, and elbow 
and wrist ? 

How many toes has the fore foot? The hind foot? 
Have the toes either claws or nails? Observe that the 
hind feet are webbed. What is the use of this? Are the 
fore feet webbed? 

Note the wide mouth, and at the posterior end the 
anus, or, more correctly, the cloacal aperture. This one 
opening serves as the outlet for the alimentary canal, kid- 
neys, and reproductive organs. 

On the dorsal side of the snout note the two small 
external nostrils, at the side of the head the eyes, and a 
little back of each eye a circular, tightly stretched patch 
of skin, the tympanic membrane, a part of the organ of 
hearing. 



THE TOAD 65 

Open the mouth and observe the tongue. What is 
there peculiar about its shape and attachment? 

Do you find any teeth? 

In the anterior part of the roof of the mouth observe 
the internal nostrils. Pass a fine probe into one of the 
external nostrils and see if it can be made to come out 
through the corresponding internal nostril. 

Just back and a little above the angle of the jaws on 
either side observe the aperture of the very short Eu- 
stachian tube, which leads into the tympanic cavity. 
Insert a probe through this aperture, and observe that 
the tympanic membrane may be pushed out. While look- 
ing at the roof of the mouth, press on one of the eyes. 
What do you see? 

On the floor of the mouth, or rather of the pharynx — 
for the posterior part of this cavity is called pharynx — 
find a median longitudinal slit, the glottis, through which 
the air passes to and from the lungs. 

Posteriorly the pharynx is continued into the esopha- 
gus. This may best be made out by pushing a large probe 
into it. 

In a living toad observe the alternate opening and 
closing of the nostrils and the elevation and depression 
of the floor of the mouth. Both movements are con- 
nected with the act of respiration; when the floor of the 
mouth is lowered air passes in through the nostrils ; when 
it is raised the nostrils are closed, and the air, being 
unable to escape, is forced through the glottis into the 
lungs. Could a frog take air into the lungs if the mouth 
were held open? Hold open the mouth and see if the 
nostrils can be closed. While the mouth is open, press 
upon the tip of the upper jaw, at the same time observing 
the nostrils. What is the effect? 

Are the eyes closed by the movement of an upper or a 
lower eyelid? Would it be possible for the toad to see 



66 ANIMAL STRUCTURES 

or to distinguish light from darkness when the eyes are 
closed? When closed tightly the eyes are pulled back 
somewhat into the head. Look at the roof of the mouth 
while this is being done. 

At the posterior end of the back, on either side of the 
middle line, observe a pulsation, due to the beating of 
the posterior lymph-hearts, situated just beneath the skin. 
(There is also a pair of anterior lymph-hearts, but they 
can not be seen from the surface.) 

Eeturn to the dead specimen, and with scissors make 
a longitudinal incision through the skin the full length 
of the body along the mid-ventral line. Observe the space 
between the skin and body, which is divided by parti- 
tions into various compartments, the subcutaneous lymph 
sinuses. Note the moisture in these, due to the presence 
of lymph, a fluid resembling blood without the red cor- 
puscles. The lymph is pumped from the sinuses into the 
veins by the lymph-hearts. 

With scissors cut through the body-wall a little to one 
side of the mid-ventral line and near the posterior end. 
An opening will thus be made into the pleuroperitoneal 
cavity, a division of the body-cavity or ccelom. Carry the 
cut forward to the anterior end of the cavity, and then 
make transverse cuts both to the right and left near the 
anterior and posterior ends of the longitudinal cut, and 
turn back the flaps thus formed. In dissecting from the 
ventral side you must bear in mind that the ventral side 
is up and the dorsal side down, that the animaPs right 
side is to your left and its left to your right. 

Insert a tube into the glottis and inflate the lungs. 
These will appear as large sacs on either side of the 
pleuroperitoneal cavity. Hold the glottis open, the air 
will pass out, and the lungs collapse, owing to the elas- 
ticity of their walls. 

Possibly a large, transparent, bilobed sac, the urinary 



THE TOAD 67 

bladder, filled with a clear fluid, may be seen at the pos- 
terior end of the pleuroperitoneal cavity. If not, insert 
a tube just within the cloacal aperture and inflate with 
air. 

The heart, situated in the middle of the body and 
near the anterior end, may still be beating. It seems to 
be in the pleuroperitoneal cavity, but is really in another 
division of the coelom, the pericardial cavity, the walls of 
which are formed by a thin, transparent membrane. 

With forceps pick up this membrane, and with scis- 
sors slit it open. The heart will now be seen more clearly. 

The posterior part of the heart is the ventricle. It is 
somewhat cone-shaped, the blunt apex being direct back- 
ward. 

Joining the base of the ventricle, and therefore 
directed forward, are the large, dark-purple right and left 
auricles. Externally these look like a single division of 
the heart, but we will see later that they are completely 
separated by an internal septum. 

Starting from the right side of the base of the ven- 
tricle and extending obliquely to the left across the auri- 
cles is the truncus arteriosus. Note that this gives off a 
right and a left branch. 

Lift up the ventricle and observe the sinus venosus, 
which is attached to the auricles. It is the same color as 
the auricles and is not quite so easily distinguished as 
the other divisions of the heart. 

The divisions of the heart beat in the following order: 
Sinus venosus, auricles, ventricle, and truncus arterio- 
sus. See if you can make this out. 

If kept moist the heart may continue to beat for sev- 
eral hours, and this even when removed from the body. 
The dissection of the heart will be taken up later. 

At either side of the heart are the large dark-red right 
and left lobes of the liver. Is either lobe subdivided into 



68 ANIMAL STRUCTURES 

smaller lobes ? Lift up the heart and see if there is any 
connection between the lobes. 

Lift up the left lobe of the liver and observe the 
stomach, the size of which varies greatly with the amount 

of food contained. Anteriorly it joins the short esopha- 
gus, while the smaller posterior end makes a U-shaped 
bend and is continued into the small intestine. The junc- 
tion between the esophagus and stomach is called the 
car dia. and the upper end of the stomach is called the 
cardiac end. while the junction between the stomach and 
small intestine is called the pylorus, and the lower end of 
the stomach the pyloric end. 

Follow out the much-convoluted small intestine. It is 
divided into two parts, the first part being the duodenum 
and last the ileum. Externally there is no marked differ- 
ence between the two. 

Posteriorly the small intestine joins the much-en- 
larged large intestine or rectum. 

Posteriorly the rectum is continuous with the cloaca, 
the external opening of which has already been seen. This 
division will be studied later. 

The long tube formed by the mouth, pharynx, esopha- 
gus, stomach, duodenum, ileum, rectum, and cloaca, is 
called the alimentary canal. 

It will have been observed that the parts of the ali- 
mentary canal within the pleuroperitoneal cavity are sus- 
pended by a thin membrane, the mesentery. 

In the mesentery suspending the small intestine look 
for a rather small, round, dark-red body, the spleen. This 
is not a part of the digestive system. 

Again, lift up the heart and observe the greenish gall- 
Madder. The color is due to the bile, a fluid secreted by 
the liver. A small duct, the bile-duct, leads from the gall- 
bladder and empties into the small intestine not far from 
the pylorus. Gently squeeze the gall-bladder. Some of 



THE TOAD 69 

the bile will be forced into the bile-duct, which can now 
be distinguished by its greenish color. Make a longitu- 
dinal slit along the intestine opposite the opening of the 
bile-duct. Again, squeeze the gall-bladder and observe 
the bile flowing into the intestine. 

Along the bile-duct in the mesentery will be seen a 
light-colored, irregular-shaped body, the pancreas. This 
secretes an important digestive fluid, the pancreatic fluid. 
In many vertebrates the pancreas has a duct of its own 
emptying into the intestine, but here the bile-duct serves 
for both liver and pancreas. 

Cut the rectum in two near its posterior end, lift it 
up and cut a little of the mesentery suspending it, observ- 
ing that the mesentery consists of two sheets of membrane 
lying side by side. These will be found to be continuous 
on the one hand with the smooth lining of the pleuro- 
peritoneal cavity, and on the other with the outer layer 
of the alimentary canal. This membrane, which lines the 
pleuroperitoneal cavity, forms the mesentery, and sur- 
rounds the alimentary canal and several other organs, is 
the peritoneum. 

Pass a probe dorsalward and forward between the lay- 
ers of the mesentery; it will enter the large subvertebral 
lymph-sinus. 

Now remove the alimentary canal by cutting the mes- 
entery and the esophagus. Slit it open along its full 
length, wash out the contents, and if possible determine 
from this the kind of food the toad lives upon. 

Carefully examine the mucous membrane lining the 
alimentary canal. Do you find any marked change in 
this in going from the stomach to the small intestine? 
or from the small intestine to the rectum? Observe that 
in the first part of the small intestine, the duodenum, the 
mucous membrane presents a velvety appearance, while in 
the posterior part, the ileum, it is thrown into longitu- 



70 ANIMAL STRUCTURES 

dinal folds. From this can you tell where the duodenum 
ends and the ileum begins? 

Eemove the liver, taking care not to injure a large 
vein, the posterior vena cava, lying dorsal to it. 

The posterior vena cava will be seen to join the sinus 
venosus. Find two large veins, the right and left ante- 
rior vence cavce, coming from toward the head and joining 
the sinus venosus on the sides. Now find the short and 
rather small right and left pulmonary veins passing from 
the lungs to the left auricle. 

Cut all of these veins, and also the branches given off 
from the truncus arteriosus, and remove the heart. 

Cut into the sinus venosus, wash out the blood, and 
find the openings of the posterior and the two anterior 
venaB cavse, and also the opening leading from the sinus 
venosus into the auricle. 

Cut away the walls of the auricles on the sides, wash 
out the blood, and observe the septum between the right 
and left auricles. Does the sinus venosus open into the 
right or into the left auricle ? 

Cut off about two-thirds of the ventricle, noting its 
thick spongy walls. Slit up the walls on either side, 
and look for an opening leading from the auricles into 
the ventricle, and another leading from the ventricle into 
the truncus arteriosus. The opening between the auricles 
and ventricle look to be single, but is really divided into 
two by the edge of the septum separating the auricles. 
To prove this, pass a probe from the right auricle into the 
ventricle and another from the left. 

Pass one blade of the scissors from the ventricle up 
into the truncus arteriosus, and cut open. Find a fold 
called the longitudinal valve hanging down into the 
truncus and partially dividii g it into a right and a left 
half. 

Look at the cut ends of the branches passing off from 



THE TOAD 71 

the truncus and observe that each is divided internally 
into three divisions. Pass fine probes down these into 
the truncus. 

Cut off about a third of the end of one of the lungs, 
and observe the central cavity and the honeycombed walls. 

Cut away the ventral wall of this and also of the other 
lung, and pass a probe forward from each into a median 
chamber, the laryngotracheal chamber, which opens out 
through the glottis, and which is kept from collapsing 
by the cartilaginous framework in its walls. 

Cut away a little of the ventral wall of the laryngo- 
tracheal chamber, pass one blade of the scissors forward 
and out through the glottis and cut. The chamber will 
now be laid open. On either side, a little back of the 
glottis, find two folds of mucous membrane extending into 
the cavity. The anterior of these are the true vocal cords, 
by the vibration of which the voice is produced; the pos- 
terior are the false vocal cords. 

If the specimen is a female, and it is near the breed- 
ing-season, a large part of the pleuroperitoneal cavity 
will be taken up by the dark-colored right and left ovaries, 
each one of which is suspended, like the intestine, by a 
double fold of peritoneum, here called the mesovarium. 
Each ovary is a sort of closed sac divided into a number of 
compartments. Tear into the ovary and, if you can, make 
this out. Note the great number of dark eggs, about the 
size of fine shot, and in addition, note the smaller, light- 
colored eggs. The dark eggs would have been laid the 
next breeding-season, the light ones a year later. Tear 
away a piece of the ovary, mount in water, and, under 
the microscope, see if you can find more than two sizes 
of eggs. 

After the breeding-season the ovaries are very much 
smaller and of a light color, but even then are quite con- 
spicuous. 



72 ANIMAL STRUCTURES 

Attached along the dorsal wall of the pleuroperitoneal 
cavity on either side observe the long, much convoluted 
oviducts. These increase greatly in size at the breeding- 
season, but are always conspicuous. Follow one of the 
ducts forward to its end, and find the opening by which 
it communicates with the pleuroperitoneal cavity. The 
opening into the cloaca at the posterior end will be seen 
later. 

As has been seen, there is no connection between the 
ovary and oviduct. When ripe the eggs break away from 
the ovaries and become free in the pleuroperitoneal cav- 
ity. They are then worked forward to the anterior end 
of the cavity, where they pass into the oviducts through 
the openings above mentioned, and then down and out 
through the cloaca. While passing through the oviduct 
they become surrounded by a white, albuminous covering. 

At the anterior end of each ovary, near its attach- 
ment, observe a yellowish body, the fat body, which is 
produced into several finger-like processes. This varies 
greatly in size, being sometimes quite small, at others 
large and conspicuous. Fat bodies are found also in a 
corresponding position in the male. 

In a male specimen observe the light-colored, elon- 
gated testes, at either side of the middle line and some- 
what nearer the posterior than the anterior end of the 
pleuroperitoneal cavity. Each testis is suspended by a 
double fold of peritoneum, the mesorchium. 

Cut off a little piece of a testis, tease in water and 
examine under the high power of the microscope. If near 
the breeding-season, the male reproductive cells, the 
spermatozoa, may be seen as small, elongated bodies. If 
taken from a fresh specimen, these will swim about act- 
ively in the water by means of the lashing of the very 
slender tail. 

Hold up the mesorchium to the light and observe a 



THE TOAD 73 

number of fine lines passing from the testis. Some of 
these are blood-vessels supplying the testis, others are 
delicate tubes, the vasa ejferentia, which carry the sperm 
from the testis to the kidney. From here the sperm passes 
out through the duct of the kidney, the ureter. 

In the position corresponding to the oviduct in the 
female observe a small, slightly convoluted white tube, the 
rudimentary oviduct. Here it is entirely functionless. 

Dorsal to the ovaries or testes, as the case may be, 
observe the elongated, flattened, dark-red kidneys. They 
are not suspended by folds of peritoneum, as are the re- 
productive organs and alimentary canal, but are covered 
on their ventral surfaces by it. 

Observe a light-colored streak, the adrenal body, ex- 
tending along the ventral surface of each kidney. They 
are not really a part of the kidneys. 

Along the outer edge of the posterior half of each 
kidney, in the peritoneum, is a duct, the ureter, which 
extends back and opens into the cloaca. They are not 
easily distinguished on account of the transparency of 
their walls. In the male, as was mentioned above, the 
ureters serve a double function, carrying off the excretion 
of the kidneys and the sperm from the testes. 

With a scalpel cut through the bone and cartilage along 
the mid-ventral line where the thighs come together and 
expose the cloaca, the posterior part of the alimentary 
canal. 

With scissors slit this open a little to one side of the 
mid-ventral line. On the ventral side find the rather large 
opening leading from the bladder, and on the dorsal side 
about opposite to this, the openings of the oviducts and 
ureters. It may not be very easy to find these. When 
found insert a fine-pointed tube into the openings of one 
of the ureters and blow in a little air. The ureter may 
now be seen distinctly. 



74 ANIMAL STRUCTURES 

Slit the sheet of peritoneum which extends from the 
outer edge of the kidne ys tc the . -wall, and continue 
the cut forward as far as possible. The large subvertebral 
lymph-sinus will be fully exposed, and along the middle 
line the vertebral column will be seen to project as a 
prominent ridge. 

Lift the kidneys and observe a number of del: 
white threads, branches of the sys- 

tem, which are distributed to the heart, the blood-vessels. 
and the various organs in the pleuroperitoneal cavity. 

Trace these branches dorsally. pulling on them gently, 
and observe that they spring from two delicate sympa- 
thetic nerves which lie along either side of the vertebral 
column and extend forward into the head. Scattered 
along each nerve are a number of slight swellings, the 
sympathetic ganglia, which, however, are rather hard to 
make out 

Coming out from the body-wall along either side of 
the spinal column are a number of white threads, the 
spinal nerves. 

The four posterior spinal nerves, the last one being 
small and inconspicuous, will I ed directly 

backward. Follow them, cutting the tissues where nee— - 
sary, and observe how they anastomose — that is. unite 
with one another. To what part of the body are they dis- 
tributed ? Are you able to trace any of the small terminal 
branche- lirectly to muscles? 

In front of the nerves just studied will be seen three 
much smaller ones going to the body-wall. 

Find a large nerve passing out to the fore leg, and two 
smaller ones, one just in front and the other just back of 
this. Do either of these unite with the large one ? 

How many spinal nerv yon find in all? 

The spinal nerves give off very short branches which 
join the sympathetic ner 



THE TOAD 75 

Before proceeding to the study of the central nerv- 
ous system examine a prepared skeleton, and observe the 
neural canal extending through the vertebral column, and 
in the skull the cranial cavity, which is continuous through 
an opening at the posterior end, the foramen magnum, 
with the neural canal. 

Eeturn to the specimen before studied. Eemove the 
skin from the dorsal side of the head, then, beginning a 
little back of the nostrils, force the point of a stout knife 
or scalpel under the bones forming the roof of the cra- 
nium, and break these away bit by bit, keeping the point in 
close contact with the bones, so as to avoid injuring the 
parts beneath. Proceed in like manner to break away 
the roof from the neural canal. 

Lining the cranial cavity and neural canal is a rather 
dark, tough membrane, the dura mater, which should 
now be pulled away. 

The central nervous system will now be exposed, con- 
sisting of the brain in the cranial cavity, and the spinal 
cord in the neural canal. 

Beginning at the anterior end, the parts of the brain 
seen from the dorsal side are: Olfactory lobes, cerebrpl 
hemispheres, thalamencephalon, optic lobes, cerebellum, and 
medulla oblongata. 

The olfactory lobes are the most anterior part of the 
brain. They are so closely joined together in the middle 
line that they seem to form a single body. Slight trans- 
verse constrictions mark the boundary between them and 
the cerebral hemispheres. 

The cerebral hemispheres lie side by side, but are sep- 
arated from each other by a longitudinal fissure. 

Posteriorly the cerebral hemispheres diverge, and 
partly enclose the median thalamencephalon. 

Next follow the rounded optic lobes, easily distin- 
guished by their dark color. 
6 



76 ANIMAL STRUCTURES 

Just back of the optic lobes is a narrow band, the 
cerebellum. 

The medulla oblongata forms the posterior division of 
the brain; it tapers slightly, and is directly continuous 
with the spinal cord, there being no distinct boundary 
between the two. 

On the dorsal side of the medulla and just back of the 
cerebellum is a triangular-shaped body, usually of a pink- 
ish color, the choroid plexus. With forceps pull this 
away. A cavity will be exposed, called the fourth ven- 
tricle of the brain. The cerebellum will now be seen more 
distinctly. 

How far does the spinal cord extend posteriorly? 

Observe a slight longitudinal groove, the dorsal fis- 
sure, extending along the median line. There is a sim- 
ilar ventral fissure along the ventral side. 

Break away the side walls of the neural canal and 
observe the union of the spinal nerves with the cord. 
Each arises by two roots, a dorsal root and a ventral root. 
These may be seen best in the large nerve passing to the 
fore leg. 

On the dorsal root observe a slight swelling, the spinal 
ganglion. 

Observe the two short olfactory nerves passing from 
the anterior end of the olfactory lobes to the nose. 

Break away the side walls of the cranial cavity, cut 
the olfactory nerves, and gently lift up the brain. On 
the ventral side and back of the hemispheres observe the 
two optic nerves passing out to the eyes. 

There are in all ten pairs of cranial nerves — that is, 
nerves given off from the brain ; but only the olfactory and 
optic will be mentioned. 

Remove the entire central nervous system, cutting the 
nerves when necessary, and place it in a small vessel of 
water. With sharp scissors cut across the brain in the 



THE TOAD 77 

regions of the cerebral hemispheres, the thalamencephalon, 
and the optic lobes. 

Look at the cut ends of the cerebral hemispheres, and 
in each observe a rather large cavity, the lateral ven- 
tricle. 

In the thalamencephalon will be found a single, me- 
dian, slit-like cavity, the third ventricle. 

In each optic lobe is an optic ventricle, while in the 
same section and ventral to the optic lobes is a small 
round opening, the iter. 

The cavity of the medulla, the fourth ventricle, has 
already been seen. 

All these cavities of the brain are continuous with one 
another, and are also continuous with the central canal 
of the spinal cord, a small canal extending through the 
full length of the cord. In order to see this, cut across 
the spinal cord and examine the cut end with a lens. 

An instructive preparation may be made by placing a 
specimen from which the skin and the contents of the 
body-cavity have been removed in 20-per-cent nitric acid 
for about twenty-four hours. The bones will be decal- 
cified, the muscles and connective tissue macerated, and 
everything may be picked away leaving the nervous system 
intact. After removing from the acid, the specimen 
should be left in running water for an hour or so to get 
rid of the acid. 

Insert the point of a scalpel through the external nos- 
tril and cut forward, opening up the relatively large nasal 
or olfactory sac with which both the external and internal 
nostril communicate. The olfactory nerve terminates in 
the cells of the membrane lining this sac. 

Examine the eye of a living toad. The exposed por- 
tion of the outer wall is the transparent cornea. Back 
of the cornea is the iris, the part that gives color to the 
eye, and in the center of the iris is a dark area, the pupil. 



78 ANIMAL STRUCTURES 

Compare the shape of this with the shape of the pupil of 
your own eye. Place the animal first in the darkness and 
then in the light. " Does the size of the pupil change ? 

In a preserved or recently killed specimen cut away 
the eyelids and remove the eye. The corners will be seen 
to be continuous with the bluish sclerotic, the part cor- 
responding to the white of our own eye. The cornea and 
sclerotic together form the outer coat of the eye. 

Attached to the back part of the eye will be found the 
ends of the eight eye muscles, by means of which the eye 
is moved. Cut these away and find the optic nerve join- 
ing the back of the eye a little distance from the center. 

With a sharp scalpel cut the eye in two a little back 
of the line where the cornea and sclerotic meet. The 
vitreous humor, a jelly-like substance, transparent in the 
recently killed specimen, will be found filling the back 
part of the eye. 

Remove the vitreous humor and observe the retina, a 
delicate membrane, pinkish in the recently killed specimen, 
gray in the preserved specimen, which forms the inner 
coat of the eye. It may be loosened every place except 
at one point where it is continuous with the optic nerve. 

Between the retina and sclerotic comes the dark 
middle coat of the eye, the choroid. This may be loosened 
from the sclerotic. 

In the front half of the eye find a relatively large, 
rather firm, spheroidal body, the crystalline lens, which 
is transparent in the recently killed toad, but opaque in 
the preserved specimen. It may have fallen out when the 
eye was first cut in two. 

The lens divides the cavity of the eye into a large 
posterior chamber, containing the vitreous humor, and a 
smaller anterior chamber, containing a clear watery fluid, 
the aqueous humor. 

Remove the lens and observe that the iris is a continu- 



THE TOAD 79 

ation forward of the choroid, and that the pupil is a hole 
in the iris. It appears black in the living animal because 
one looks through it into a dark chamber. 

The tympanic membrane and tympanic cavity have 
already been seen. The essential part of the organ of 
hearing, the membranous labyrinth or internal ear, is a 
complicated structure located within the bones of the head, 
and is difficult to dissect. 

In order to study the blood-vessels it will be necessary 
to inject the arteries. This is easily done, the only instru- 
ment necessary being an ordinary medicine-dropper, 
although an injecting syringe is a little better. 

Kill the animal with chloroform and open the pleuro- 
peritoneal cavity to the left of the mid-ventral line as 
in the previous dissection, taking especial care not to cut 
the anterior abdominal vein, which is attached to the body- 
wall along the mid-ventral line. Inflate the lungs, slit 
open the pericardium. With scissors make a longitudinal 
cut through the tip of the ventricle. Fill the medicine- 
dropper with the injection-mass and insert the end 
through the ventricle into the truncus arteriosus. Hold 
the ventricle with the thumb and finger of the left hand 
so that the injection-mass will not escape, and gently 
squeeze the bulb. When empty the dropper may be with- 
drawn, refilled, and the operation repeated. From one 
to three droppers full will be enough, depending upon the 
size of the specimen. When through, tie a string around 
the ventricle so as to prevent the escape of the injection- 
mass. The specimen should be left for a few hours for 
the injection-mass to set. Before doing this, however, 
tie one of the lungs in two places near the base and remove 
it by cutting between the ligatures. After it has dried 
cut it in two and observe the blood-vessels in its walls. 

After the injection-mass has set cut through the 
shoulder girdle, the part of the skeleton to which the 



80 ANIMAL STRUCTURES 

fore legs are attached, along the median line, lift up the 
cut ends, and observe a number of veins and arteries 
going to and from the heart. The arteries are the ones 
filled with the injection-mass, while the veins are filled 
with blood. Expose these vessels still further by cutting 
away some of the muscles and the membrane around the 
base of the heart, using great care not to cut any of the 
veins, for in that case the blood would escape, and it 
would then be almost impossible to follow them. 

Pull the heart to the right and find the large left ante- 
rior vena cava, which, as has been seen before, empties 
into the sinus venosus. Follow this anteriorly a short 
distance, and observe that it is formed by the union of 
three veins: the external jugular, which may be traced 
straight forward for a little distance; the subclavian, com- 
ing from the fore leg; and between these the innominate, 
extending upward and forward. Trace these as far as you 
can. It will be seen that each is formed by the union of 
still smaller veins. Work out the anterior vena cava and 
its branches on the right side. They will be found the 
same as on the left. 

Xow carefully free the anterior abdominal vein from 
the body-wall, observing that it receives branches from 
the body-wall and also from the bladder. At the poste- 
rior end of the pleuroperitoneal cavity it will be seen to 
arise from the union of a right and left pelvic vein, which 
will be studied later. Anteriorly it divides into right and 
left branches, which enter the corresponding lobes of the 
liver. 

Lift up the intestine, and in the mesentery notice the 
arteries and veins which supply the alimentary canal, 
spleen, and pancreas. The veins unite to form a large 
trunk, the portal vein, which may be traced to the liver, 
where, like the branches of the anterior abdominal vein, it 
breaks up into capillaries. Thus the liver receives venous 



THE TOAD 81 

blood both from the anterior abdominal vein and from 
the portal vein. When veins thus break up into capillaries 
within an organ it is called a portal circulation. In the 
case of the liver it is called the hepatic portal circulation. 
As will be seen later, the liver also receives arterial 
blood. 

Cut the mesentery suspending the rectum and between 
the kidneys observe the large posterior vena cava, arising 
by the union of the short renal veins from the kidneys. 
Trace the posterior vena cava forward to its union with 
the sinus venosus, observing that it receives large hepatic 
veins from the liver. 

The pulmonary veins, returning blood from the lungs, 
have already been seen, but should be again observed. 

Along the outer edge of each kidney observe a rather 
large renal portal vein, the blood from which enters the 
kidney, thus forming another portal circulation, in this 
case called the renal portal circulation. The kidneys also 
receive arterial blood. Observe that there are veins enter- 
ing the renal portal from the side. 

Follow one of the pelvic veins from the point where 
it unites with its fellow to form the anterior abdominal, 
dorsalward. It will be seen to be connected with the renal 
portal. Actually both the renal portal and the pelvic are 
branches of the femoral vein, a large vein returning blood 
from the hind leg. Thus part of the blood returning 
from the leg passes through the renal portal vein to the 
kidney, and part through the anterior abdominal vein to 
the liver. The sciatic, another vein returning blood from 
the leg, unites with the renal portal. 

The arteries will be found much easier to study than 
the veins. Those given off from the heart are already well 
exposed. Each branch given off from the truncus arteri- 
osus will be seen to divide into three arteries, the ante- 
rior of which is the carotid trunk, the middle the 



82 ANIMAL STRUCTURES 

aortic trunk, and the posterior the pulmo-cutaneous 
trunk. 

Follow the pulmo-cutaneous trunk a short distance, 
and observe that it divides into two branches, the short 
pulmonary artery going to the lung, and the cutaneous 
artery which supplies the skin. Follow this to a point a 
little back of the tympanic membrane. Now make a longi- 
tudinal incision through the skin along the mid-dorsal 
line, free it from the body, and find a large branch of 
the cutaneous artery running backward in the skin along 
the side of the body. Follow this forward to its union 
with the main cutaneous artery. 

The carotid trunk will be seen to divide into two 
branches, a smaller lingual artery passing directly for- 
ward to the tongue, and a larger carotid artery which 
bends dorsally around the pharynx. Just at the begin- 
ning of the carotid artery there is a slight enlargement 
called the carotid gland. Now cut through the angle of 
the jaws, loosen the mucous membrane from the roof of 
the mouth, and observe that the carotid runs forward a 
little distance just beneath the mucous membrane. 

Trace the aortic trunk around to the dorsal side of 
the esophagus, and then backward to its union with the 
aortic trunk of the opposite side. Each aortic trunk gives 
off three branches: the short vertebral artery, which enters 
the body-wall and sends branches forward and backward 
along the vertebral column; the subclavian artery , which is 
given off close to the vertebral and which supplies the 
fore leg; and the esophageal artery, which supplies the 
esophagus. Trace out the branches of the subclavian. 

Posteriorly the two aortic trunks unite to form the 
dorsal aorta, which runs backward along the middle line. 
Just where the aortic trunks unite, the large cceliaco-mes- 
enteric artery is given off. Trace this out into the mesen- 
tery. What organs does it supply ? Farther back the dor- 



THE TOAD 83 

sal aorta gives off several branches which supply the kid- 
neys and the reproductive organs. Posteriorly it divides 
into two branches, the right and left iliac arteries. Trace 
one of these out and find what parts it supplies. 

In addition to the arteries and veins there are myriads 
of very fine vessels, called capillaries, through which the 
blood flows from the small arteries into the small veins. 
They may be seen in the tail of a tadpole, and here it is 
only necessary to place the animal in a watch-glass and 
bring it under the compound microscope. But as tad- 
poles can be had only at certain times of the year, it will 
likely be necessary to use the web of a frog's foot, the web 
of a toad's foot being too thick. 

Take a thin board 2 or 3 inches wide and 6 or 8 
inches long, and cut a wide notch in one end. Wrap a 
frog in a piece of cloth so it will not be able to struggle, 
leaving one hind leg out. Tie threads to two of the toes, 
place the animal on the board, pull the threads around on 
the opposite side of the board so that the web is stretched 
over the notch, and tie. Xow bring the web under the 
microscope. The arteries may be distinguished from the 
veins by the fact that in the arteries the blood flows from 
larger vessels into smaller, while in the veins it flows from 
smaller vessels into larger. The capillaries are the vessels 
connecting the smallest arteries with the smallest veins. 
They are usually just large enough to allow the corpus- 
cles to pass through single file. 

The skeleton of the toad is made up of a large number 
of bones and cartilages, some of which are movably, others 
immovably, articulated with one another. It is on the 
inside of the body, and is hence known as an endoskele- 
ton. In the present description only the more general 
features of the skeleton will be noted. 

Eemove the skin and viscera from a toad and then 
clear away the muscles. This is rendered easy by occa- 



84 ANIMAL STRUCTURES 

sionally dipping the specimen into boiling water. Be care- 
ful not to separate any of the bones. However, the 
shoulder-girdle to which the fore legs are attached will 
come away, as it is not articulated to the rest of the 
skeleton, being held in place by muscles. After the skele- 
ton has been pretty well cleaned allow it to dry for a few 
hours. This will bring out the individual bones much 
more clearly. 

Observe that the backbbone is made up of a number of 
separate pieces called vertebrae. How many are there? 
Given off from the sides of a vertebra are the long trans- 
verse processes. Do they occur on every vertebra? The 
neural canal extending through the vertebrae has already 
been seen. Find the openings between the vertebrae along 
the sides through which the spinal nerves pass. The pos- 
terior part of the vertebral column is not segmented, but 
consists of a long, rod-like bone, the urostyle. 

Has the toad any ribs? 

In the skull, or skeleton of the head, observe the upper 
and lower jaws, the latter of which is movably articulated 
with the rest of the skull. 

The brain-case, containing the cranial cavity, has 
already been seen. At either side of the brain-case is a 
large round opening where in life the eyes are situated. 
In front of the brain-case are the nasal capsules, in which 
the olfactory sacs are lodged, and joining the posterior 
end of the brain-case at right angles are the auditory cap- 
sules, in which the- internal ear is located. 

Break away the skull from the vertebral column, and 
at the sides of the lower part of the foramen magnum, 
or opening through which the cranial cavity communi- 
cates with the neural canal, observe two oval prominences, 
the occipital condyles, which fits into corresponding de- 
pression in the first vertebra. 

The different divisions of the skull are made up of 



THE TOAD 85 

a number of separated bones and cartilages which may 
be separated by boiling. 

The shoulder-girdle will be seen to be made up of 
several closely united bones and cartilages. 

At either side of the shoulder-girdle is a cup-shaped 
depression into which fits the rounded head of the 
humerus or first bone of the fore leg. Following the 
humerus is the radio-ulna, a bone that has been formed 
by the fusion of two bones lying side by side. Do you 
find any indication of this fusion? Next comes the 
carpus, or wrist, which is made up of several small bones. 
How many? Following the carpus are the four metacar- 
pals, corresponding to the bones of the palm ; and follow- 
ing these are the phalanges, or bones of the fingers. How 
many pieces are there in each finger ? 

Articulated with the transverse processes of the last 
vertebra is the hip-girdle, which has something the shape 
of the wish-bone of a chicken. This is made up of several 
bones immovably articulated with one another. 

The first bone of the hind leg is the femur. Following 
the femur comes the tibio- fibula, which, like the radio-ulna, 
has been formed by the fusion of two bones. The tarsus, 
or ankle, is made up of two long bones followed by two 
very small bones. Following the tarsus are the five meta- 
tarsals lying side by side, and following these are the 
phalanges, or bones of the toes. How many pieces are 
there in each toe? 



SUGGESTIONS TO TEACHEES 

The success of a laboratory course in zoology, as well 
as the peace of mind of the teacher, depends to no in- 
considerable extent upon having at hand an abundance 
of material, and having it just at the time it is needed. 
For this reason it is well to lay in a supply of the differ- 
ent forms considerably in advance of the time they are 
to be used, and it is all the better if this can be done at 
the very beginning of the year. Most of the forms needed 
are widely distributed, and may be found in any locality, 
but where this is not the case they may be had from 
regular dealers in laboratory materials. The ideal way 
would be to have each student collect, and, when neces- 
sary, preserve his own material, but in practise this does 
not always work well. However, it is an excellent plan 
to take the entire class out and have them help with the 
collecting. In this way they learn where and how the 
material is obtained, and will not have to think of a 
hydra, for instance, as an animal found exclusively in a 
certain aquarium in the laboratory. 

The cell. — In Chapter I a study of the blood-cor- 
puscles and a few other cells has been introduced, partly 
for the sake of a knowledge of the cells themselves and 
the aid it will give in understanding the Amoeba and 
Paramcecium, and partly that the student may learn to 
use the microscope in studying objects that are easily 
found, and which can be studied at rest. If the teacher 
so desires, a few plant-cells may be shown in connection 
with this work, such as the cells in the hairs of flowers, 
the leaves of moss, and the filaments of Spirogyra. 

87 



88 SUGGESTIONS TO TEACHERS 

The Amoeba. — Amoebae may occur in the mud and 
ooze of almost any body of fresh water, and are often 
found in the most insignificant puddles where water 
trickles out from a spring or a hydrant. Yet they are not 
always easy to get just at the time they are wanted. Be- 
sides this, they are always relatively scarce, never increas- 
ing with that amazing rapidity characteristic of the in- 
fusoria. 

Fill a dozen or more shallow dishes with water, mud, 
ooze, dead leaves, etc., from the bottom of a pond or 
puddle of water, and allow these to stand in the laboratory 
for a day or two. In all probability, some of the dishes 
will be found to contain Amoebae. It is well for the 
teacher to find an Amoeba and show it to the students 
before setting them to look for the animals themselves. 

Paramcecium. — If a jar be filled with water and water- 
weeds, either dead or alive, from any pond or stream, 
and allowed to stand until putrefaction sets in, a number 
of different kinds of infusoria will appear, first one kind 
predominating, and then another. Among these, though 
not the first to appear, will be the Paramoecium. The 
process of putrefaction may be hastened by adding a very 
small piece of meat, though this is not usually necessary. 
In order to be sure of plenty of material when wanted, 
cultures such as those described above should be started 
about three weeks before the time when they are to be 
used, and others later, a new one every two or three days. 
This is necessary, because one can not be sure just how 
long the Paramoecia will be in coming, that depending 
upon the temperature and other conditions; and further, 
because after they do come, they may not remain indefi- 
nitely; what was a fine culture at one time often being 
found worthless a few days later. Then, too, if a cul- 
ture be examined from day to day, it will be found that 
at one time multiplication is very rapid, every slide exam- 



SUGGESTIONS TO TEACHERS 89 

ined showing dividing individuals, while later division will 
almost cease, and instead numerous cases of conjugation 
will occur. In order that the class may observe both these 
processes it will be necessary to have cultures in different 
stages at the same time. 

After Paramoecia have appeared in the earlier cultures 
new ones may be hastened by pouring a little water from 
one of the old cultures into the new one. 

It would be well to have each student start a culture 
of his own, and observe the progress of putrefaction, and 
the various kinds of animals that appear. Only a very 
short time each day need be given to this. It might be 
well for the teacher to state in advance that he will not 
undertake to give the name of every creature found. 

In almost every Paramoecium slide studied there will 
be numerous bacteria, and although these are plants and 
not animals, the attention of the students should be called 
to them, on account of the general interest attached to 
them. 

Hydra. — Hydra are widely distributed, and may be had 
in almost any locality. They are found attached to sticks, 
dead leaves, algae, and in fact to almost anything in 
fresh-water ponds and pools and in quiet portions of 
streams. Although so widely distributed, they are by no 
means present in every pool or streani, and one may have 
to search some time before finding them. When found 
they may occur in such numbers that there will be thou- 
sands in a pool a few yards square, every stick or weed 
in it being covered with them, but usually they are far 
less abundant, and may escape the notice of even an ex- 
perienced collector. 

If you have not had experience in collecting, start out 
with a number of glass jars — the more the better — and 
wherever you come to a quiet pool, place a handful of 
weeds, sticks, etc., in one of the jars, together with a 



90 SUGGESTIONS TO TEACHERS 

little water. Label each jar, so that in case it is 
found to contain Hydra you may know from what pool 
it came. 

On returning to the laboratory, add enough water to 
each jar to fill it, and after it has stood for a few hours 
or a day or two, examine the surface of the water and 
the sides of the jar for Hydra. 

Fortunately Hydra thrive and multiply rapidly in an 
aquarium, so that, starting with even one or two indi- 
viduals, in the course of three or four weeks there may 
be enough for a large class. In one instance where a 
record was kept, a Hydra began producing buds the third 
day after breaking away from the parent, and ten days 
later had produced ten new individuals. 

If placed in a jar of pure water containing small 
Crustacea for food and a few green water-plants, such as 
Chara or Spirogyra, Hydra may be kept in the laboratory 
indefinitely. There is danger, however, that putrefaction 
may set in and kill them, so that in case your supply is 
limited and you are keeping them for class work, it will 
be well to change the Hydra to a fresh vessel of water 
every five or six days, being careful always that there are 
plenty of small Crustacea for food. These may be caught 
in troughs or pools with a small net made of fine cheese- 
cloth. 

It would be an excellent plan to have each student 
keep one Hydra under observation for a number of days 
or weeks, noting the length of time required for a bud 
to develop and the number of buds produced, and keep- 
ing a sharp lookout for the formation of reproductive 
structures. It would also be well to observe the renewal 
of lost parts. For this purpose place the Hydra in a shal- 
low vessel of water with wax or paraffin in the bottom, 
and with a sharp scalpel cut some of them in two cross- 
wise, others lengthwise, or, better, cut them for only 



SUGGESTIONS TO TEACHERS 91 

half or two-thirds of their length, so that a two-headed 
Hydra will be produced. 

To show the process of feeding, get a number of 
Hydra hungry by keeping them for two or three days in 
a vessel containing nothing but water. Then let each 
student transfer one of them to a watch-glass contain- 
ing a little water and a few small Crustacea. 

The Starfish. — Starfish are exclusively marine ani- 
mals, as are all the Echinoderms, the group to which 
the Starfish belong; consequently the living animals 
can be studied only at the seashore. Most teachers will 
therefore have to depend for material upon the dealers 
in laboratory supplies. It is well to have, in addition to 
the specimens preserved in alcohol or formalin, a few 
dried specimens, as these may be used year after year for 
the study of some of the external features. 

Starfishes are usually easily collected, as they live near 
the shore, and are found at low tide, either exposed or 
in shallow water. They are killed by leaving them for 
a few hours in fresh water. Before placing them in the 
hardening fluid, either formalin or alcohol, cuts should 
be made in one or two of the rays, so that the fluid may 
reach the soft internal organs. If alcohol is used they 
may be left in 70-per-cent for a day or two, and then 
transferred to 85-per-cent. 

The Earthworm. — Perhaps no animals studied in the 
laboratory are so easily obtained as earthworms. They 
occur in every locality, and may be found almost anywhere 
by digging in moist earth. As is well known, they come 
to the surface after a rain, and they also come to the 
surface at night, when they may be collected by the aid 
of a lantern. 

For dissection, as large specimens as possible should 
be selected. Two different methods may be employed in 
killing them, one slowly with alcohol and the other with 



M SOGGESmOHS IC XKACHKBS 

boiling water. In the first ease r place the worms in a 
flat pan with enough water to cover them well. Then 
with a medicine-dropper slowly add alcohol until 
are killed. This should occupy an hour or more. With 
the second method, drop the worms into a vessel con- 
taining enough water almost up to boiling-point to cover 
them. In a few seconds — tha: k soon as the worms 
are dead — pour in a large quantity of cold water. This 
method may seem cruel, hut it is not so. since death is 
almost instantaneous. Whichever way they are killed 
they should next he carefully stretched out, one by one, 
in 70-per-cent alcohol and held in this position until 
they show no inclination to curl up. After a few honrs 
they should he transferred to 85-per-cent alcohol and 
left for twenty-four hours. They should then be put 
into 95-per-cent alcohol for three or four days, and final- 
ly hack into 85-per-cent, where they may be kept indefi- 

b the worms may he studied at a time of year when 
living specimens are not aece^ible, a number should be 
placed in a box or jar of earth, which should he kept 
moist and in a place where it will not freeze. The tend 
must he kept covered to prevent the worms from - - 

Cut a few segments off the anterior end of some 
worms and off the posterior end of others, and keep 
them in loose moist earth for several weeks to see the 
:t:t:t:::::: :_ :lr _:s: 7:11-5. 

At the beginning of the year take the class out to 
look for egg capsules. These are usually found without 
difficulty by looking through shovelfuls of earth in wh 
worms abound. Some may be placed in a bottle :: al- 
cohol for future use, others opened and their contents 
examined, and still others kept in a bottle of loose earth 
and observed from time to time until the young worms 



SUGGESTIONS TO TEACHERS 93 

hatch. This may help to overcome the prejudice which 
so many feel toward worms. 

Do not fail to read Darwin's Vegetable Mould and 
Earthworms, and, if possible, have the students read it 
also. 

The Crayfish. — Crayfish are absent in the New Eng- 
land States east of the Housatonic Eiver as well as in 
the Great Plains to the east of the Kocky Mountains 
and in Southern California. In most other parts of the 
United States they are found in abundance. They may 
be obtained by turning over stones in the bottoms of 
sluggish streams. To kill a crayfish pass a scalpel for- 
ward under the carapace into the pericardial sinus and 
allow them to bleed to death. Before preserving, break 
away a little of the posterior part of the carapace, so 
that the fluid may reach the internal organs. Either 
formalin or alcohol may be used. If the latter, place 
the animals in 70-per-cent for a day or two and then 
transfer them to 85-per-cent. 

Crayfish may be kept alive in the laboratory for a 
long time, in which case it should be so arranged that 
they may stay in the water or out of it as they choose. 
They will eat meat, worms, etc. They may be trans- 
ported for long distances. Some were bought in the 
market at Portland, Ore., and shipped in a box to cen- 
tral California, being three or four days on the way. Sev- 
eral died soon. Others were kept alive for almost two 
months. 

Along the seaboard and in cities, lobsters may be 
used instead of crayfish, as their structure is almost the 
same. 

If crabs are available it is an excellent training to 
have the students study these for a little while without any 
aid from books, noting the resemblances and differences 
between them and the crayfish. 



94 SUGGESTIONS TO TEACHERS 

The teacher should by all means have Huxley's The 
Crayfish: An Introduction to the Study of- Zoology. 

The Grasshopper. — Grasshoppers are usually abun- 
dant in the fields during the summer and fall, so that no 
difficulty will be experienced in finding them. If they 
are to be dissected in the winter it will be well to have 
the students observe the living animals in advance. Kill 
them by placing them in a tight jar with a piece of cot- 
ton saturated with chloroform, or, better, by immersing 
them for a few seconds in water that is almost boiling. 
Then place them for a day in 70-per-cent alcohol, first 
making an incision through the body-wall to the side of 
the mid-dorsal line. Those intended especially for the 
study of the external features need not be slit. Next 
transfer them to 85-per-cent alcohol, using a relatively 
large quantity, and stirring them about in it a few times 
during the first two or three days. 

It would be well for the teacher to have for reference 
The Anatomy of the Carolina Locust, by Prof. Robert E. 
Snodgrass, published by the Washington Agricultural Col- 
lege, Pullman, Wash. 

The Fresh-Water Mussel. — Fresh-water mussels are 
found partly buried in the sand and mud in the quiet 
portions of rivers and large creeks, and also in lakes and 
ponds where the water stands the year round. They 
may be easily drawn out with a garden rake. For- 
malin is an excellent hardening and preserving agent for 
mussels. Before they are placed in it insert a wooden 
wedge between the valves, so that the fluid will reach 
the body. 

Mussels are quite tenacious of life, and may be trans- 
ported long distances out of water. They may be kept 
alive for months in an aquarium with mud in the bottom 
in which they can bury themselves. The water should 



SUGGESTIONS TO TEACHERS 95 

be changed every week or two unless there is a large 
quantity, in which case no change w r ill be necessary. 

The Toad. — Toads and frogs are very much alike, and 
it makes little difference which is used, the directions for 
dissecting the one answering in almost every particular 
for the other. We have chosen the toad because in our 
experience they are more easily obtained than frogs. 
Toads conceal themselves during the day, but come out 
at dusk in search of food. If one walks about in a gar- 
den or along the streets of a village or in the suburbs 
of a city in the early evening he is almost sure to find 
a number. When it becomes too dark to see them they 
may be detected by the rustling of the grass as they hop 
about. Often a good place to find them is in the street 
under the electric light. During the breeding-season in 
the spring they go to the ponds and streams, where they 
may be found in numbers, and where their dark-colored 
eggs may also be found enclosed in transparent albumi- 
nous strings several feet long. 

Fresh specimens are better for dissection than pre- 
served ones, but it is well, nevertheless, to have a stock 
of preserved material on hand. The toads should be 
killed by placing them in a tight jar with a piece of cotton 
saturated with chloroform. They may be hardened in 
either formalin or alcohol. If the latter is used, place 
them first in about 50-per-cent or 60-per-cent for a day, 
and then transfer them to 70-per-cent, using a relatively 
large quantity of this, and moving them about in it two 
or three times in the course of the first three or four 
days. Before placing the specimens in the formalin or 
alcohol cut into the body-cavity, so that the fluid may 
readily reach the internal organs. 

Toads may be kept alive in a box of moist earth set 
away in a cool place, but if the earth is allowed to dry 
up they will soon die. They may be fed by placing in- 



96 SUGGESTIONS TO TEACHERS 

sects, such as beetles, in the box with them. If the box 
were placed in a cellar in the fall it is likely that the 
toads would stay alive so that they might be used for 
dissection at any time during the winter, but we have 
never tried this. 

Microscopes. — It is highly desirable that there should 
be a compound microscope for each student, and where 
this is not possible the number should approach this as 
nearly as may be. Fairly satisfactory instruments may 
be had at a comparatively small cost, but the better 
grades give better satisfaction, and are cheaper in the 
long run. 

Dissecting microscopes are a great convenience; but 
where only a limited amount of money is available for 
laboratory equipment it is better to spend it for com- 
pound microscopes, as hand lenses can be made to take 
the place of the dissecting microscopes. 

Dissecting Pan. — Each student should be provided 
with a dissecting pan, having in the bottom a layer of 
about half an inch of paraffin or beeswax, which may be 
run in while melted. Some device for holding the wax 
in place will be necessary, and for this a wire placed 
diagonally across the bottom and soldered at both ends 
will answer. A convenient size of pan is one nine inches 
long by six inches wide and two inches deep, with flaring 
sides and ends, although the exact size and shape make 
little difference. 

Miscellaneous Supplies. — A few wide-mouthed fruit- 
jars of various sizes will be found convenient for collect- 
ing, for aquaria, and for storing preserved material. A 
few glass tumblers and sauce-dishes will be found useful 
for various purposes. 

A good injection-mass is easily made as follows: 
Place about half a pound of white glue in a vessel, and 
add considerably more than enough water to cover it. 



SUGGESTIONS TO TEACHERS 97 

Allow this to stand for several hours. To a saturated 
solution of bichromate of potassium, a quart or more, 
add an equal volume of a saturated solution of acetate 
of lead. A bright yellow precipitate will form. Allow 
this to settle, and then pour off the fluid. Now pour 
off the water from the white glue, and melt it in a double 
boiler — one of the kind used in cooking will answer ad- 
mirably — and stir in the precipitate. It will be well also 
to stir in a few drops of carbolic acid to keep the mass 
from molding. This material may be kept indefinitely. 
When used it must be heated, always using the double 
boiler. 

Methyl green comes in the form of a powder. It is 
prepared for use by making a strong solution in water 
and adding a little acetic acid, about 1 per cent. 

Alcohol and formalin are the two fluids used for pre- 
serving material. They should both be used in relatively 
large quantities. The strength of alcohol to be used is 
given in connection with the directions for preserving 
the different animals. Formalin is generally used in 2- 
per-cent solution, which is made by mixing one part of 
commercial formalin with nineteen parts of water. Thus, 
with one quart of formalin, five gallons of the preserv- 
ing fluid can be made. It is well to wash specimens pre- 
served in formalin in running water for a while before 
they are given out for dissection. 

In addition to the articles already mentioned the fol- 
lowing will be needed: Some caustic potash, a small 
bottle of acetic acid, a large bottle of nitric acid (the 
cheap, crude acid answering very well), and a bottle of 
carmine, which comes in the form of small lumps or 
powder. 

It is an excellent plan for the teacher to illustrate 
by the use of models the structure of such forms as the 
Amoeba, Paramoecium, and Hydra, and also some of the 



98 SUGGESTIONS TO TEACHERS 

more difficult points in the anatomy of other animals. 
For making these, nothing is so satisfactory as composite 
clay, a material that never dries, is always ready for use, 
and may be used over and over for years. It is also 
well to have the students do some modeling, as this fixes 
structure even better than by drawing. The clay may 
be had of the C. H. Chavant Manufacturing Company, 
Jersey City, N. J., and probably elsewhere. It is not ex- 
pensive, and every teacher should have at least a few 
pounds. 

Each student should be provided with a drawing-book, 
a note-book, a drawing pencil, a scalpel, a pair of fine 
pointed scissors, a pair of fine forceps, two dissecting 
needles, one or two seekers made of bristles tipped with 
sealing-wax, a medicine-dropper, a few slides and cover- 
glasses, a watch-glass, and a hand lens. The cheap tri- 
pod form of lens is a good kind, as it may be used instead 
of a dissecting microscope. 

The order in which the different forms should be 
taken up is largely a matter of convenience and personal 
preference. 

The method of beginning with the simpler forms and 
going to the more complex has been pursued, but there is 
no important reason why this order should not be 
changed if the teacher so desires. 

No matter how well the teacher may be acquainted 
with the forms taught, he should spend at least a little 
time in going over the laboratory work in advance of 
the class. 

Here, as elsewhere, it is not so much the amount of 
work that counts as the thoroughness with which it is 
done, and the skill of the teacher will show best in his 
ability to keep the students working and interested in a 
thing until it is thoroughly understood. 

No attempt has been made to indicate the number of 



SUGGESTIONS TO TEACHERS 99 

drawings that should be made, this being left to the judg- 
ment of the teacher; but in general all the important 
structures should be carefully drawn. However, the 
object of this is not for the sake of the drawings them- 
selves, but to enable the student to see accurately. No 
one should be discouraged because he finds it hard to draw. 

David Starr Jordan. 
George Clinton Price. 

Stanford University, 
June 1, 1903. 



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Plant Studies. 

An Elementary Botany. i2mo. Cloth, $1.25. 

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A First Book of Botany. i2mo. Cloth, $1.10. 

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A Laboratory Manual of Botany. 

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Seed Plants. Part I. Morphology of Spermatophytes. By 
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The Twentieth Century Botanical Course is now complete. 
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The Garden's Story; or, Pleasures and Trials 
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The Origin of Cultivated Plants. 

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Flowers and their Pedigrees. 

By Grant Allen. Illustrated. i2mo. Cloth, $1.50. 

The Story of the Plants. 

By Grant Allen. With Many Illustrations. i6mo. 
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A Contribution to our Knowledge of Seedlings. 

By Sir John Lubbock, Bart. 684 Illustrations. 2 vols., 
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A Study of Leaves. 

By Mary B. Dennis. Small 410. In colors. Paper, 
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4 1903 



